Reactions of an Isolable Dialkylsilylene with Aroyl Chlorides

molecules

ArticleArticle Reactions of an Isolable Dialkylsilylene with Aroyl ReactionsArticle of an Isolable Dialkylsilylene with Aroyl Chlorides.ReactionsChlorides. of A A anNew New Isolable Route Route Dialkylsilyleneto to Aroylsilanes Aroylsilanes with Aroyl

Xu-QiongChlorides.Xu-Qiong Xiao, Xiao, Xupeng Xupeng A NewLiu, Liu, Qiong Qiong Route Lu, Lu, Zhifang Zhifang to Li LiAroylsilanes *, *, Guoqiao Guoqiao Lai Lai and and Mitsuo Mitsuo Kira Kira * *

Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Xu-QiongKey Laboratory Xiao, Xupeng of Organosilicon Liu, Qiong Chemistry Lu, Zhifang and Material Li *, TechnologyGuoqiao Lai of Ministryand Mitsuo of Education, Kira * HangzhouHangzhou Normal Normal University, University, Hangzhou Hangzhou 311121, 311121, China; China; xqxiao [email protected]@hznu.edu.cn (X.-Q.X.); (X.-Q.X.); [email protected]@163.com Laboratory of Organosilicon (X.L.) (X.L.);; [email protected] [email protected] Chemistry and (Q.L.);Ma (Q.L.);terial [email protected] [email protected] Technology of Mini (G.L.) (G.L.)stry of Education, *Hangzhou * Correspondence:Correspondence: Normal University,[email protected] [email protected] Hangzhou 311121, (Z.L.); (Z.L.); China; [email protected] [email protected] [email protected] (M.K.); (M.K.); (X.-Q.X.); Tel.: +86-571-2886-7825 (Z.L.) [email protected].: +86-571-2886-7825 (X.L.) (Z.L.); [email protected] (Q.L.); [email protected] (G.L.) * Academic Correspondence: Editor: Derek [email protected] J. McPhee (Z.L.); [email protected] (M.K.); Academic Editor: Derek J. McPhee Received:Tel.: +86-571-2886-7825 14 September 2016;(Z.L.) Accepted: 8 October 2016; Published: 15 October 2016 Received: 14 September 2016; Accepted: 8 October 2016; Published: date AcademicAbstract: Editor:The reactions Derek J. McPhee of isolable dialkylsilylene 1 with aromatic acyl chlorides afforded aroylsilanes Abstract:Received:3a–3c exclusively. 14The September reactions Aroylsilanes 2016; of isolable Accepted3a dialkylsilylene–: 3c8 Octoberwere characterized 2016; 1 with Published: aromatic by date1H-, acyl 13 C-,chlorides and 29 Si-NMRafforded spectroscopy,aroylsilanes 3ahigh-resolution–3c exclusively. massAroylsilanes spectrometry 3a–3c were (HRMS), characterized and single-crystal by 1H-, 13C-, molecularand 29Si-NMR structure spectroscopy, analysis. high-resolutionAbstract:The reaction The reactions mechanisms mass spectrometry of isolable are discussed dialkylsilylene (HRMS), in comparison and 1 withsingle-crystal aromatic with related acylmolecular reactionchlorides structure of afforded1 with analysis. chloroalkanes aroylsilanes The reaction3aand–3cchlorosilanes. exclusively. mechanisms Aroylsilanes are discussed 3a– 3cin comparisonwere characterized with related by 1H-, reaction 13C-, and of 1 29withSi-NMR chloroalkanes spectroscopy, and chlorosilanes.high-resolution mass spectrometry (HRMS), and single-crystal molecular structure analysis. The reactionKeywords: mechanismsdialkylsilylene; are discussed silyl ketone; in comparison acylsilane; with insertion; relatedX-ray reaction analysis of 1 with chloroalkanes and Keywords:chlorosilanes. dialkylsilylene; silyl ketone; acylsilane; insertion; X-ray analysis

Keywords: dialkylsilylene; silyl ketone; acylsilane; insertion; X-ray analysis 1. Introduction 1. IntroductionAcylsilanes or α-silyl ketones have been known as a unique class of silicon compounds [1–9], showing remarkably red–red shifted n→π* transition bands [1,2] and being useful as distinct reagents 1. IntroductionAcylsilanes or α-silyl ketones have been known as a unique class of silicon compounds [1–9], showingin organic remarkably synthesis [red–red4–6,10– 19shifted]. Most n→ ofπ all,* transition acyltris(trimethylsilyl)silanes bands [1,2] and being are useful of particular as distinct importance, reagents inwhich organicAcylsilanes were synthesis utilized or [4–6,10–19].α-silyl for the ketones synthesis Most have of ofall, been the acyltris ﬁrstknown(trimethylsilyl)silanes stable as a silicon–carbon unique class areof doubly silicon of particular bonded compounds importance, compounds [1–9], whichshowing(silenes) were remarkably [20 utilized,21]. However, forred–red the thesynthesis shifted synthesis n →ofπ the* of transition acylsilanesfirst stable bands issilicon–carbon still [1,2] limited and bein because doublyg useful ofbonded as the distinct relatively compounds reagents facile (silenes)insilicon–carbon organic [20,21]. synthesis bondHowever, [4–6,10–19]. cleavage the synthesis underMost of the all, of reaction acyltrisacylsilane(trimethylsilyl)silanes conditions.s is still limited The direct because are reaction of ofparticular the of arelatively silylmetal importance, facile with silicon–carbonwhichan acyl were halide utilized bond afforded cleavagefor the the synthesis correspondingunder the of reaction the acylsilanes,first cond stableitions. silicon–carbon but The the yieldsdirect reactiondoubly were usually bonded of a silylmetal low compounds due towith the an(silenes)undesired acyl halide [20,21]. secondary afforded However, reactions the the corresponding synthesis [22,23]. of The acylsilaneacylsila oxidationnes,s isbut of stillα the-silyl limited yields alcohols because were using usually of the ordinary relativelylow due oxidizing to facile the undesiredsilicon–carbonreagents oftensecondary bond leads cleavage toreactions the corresponding under [22,23]. the The reaction aldehydes oxidation cond [5 itions.].of The α-silyl ﬁrstThe successfulalcoholsdirect reaction using synthesis ofordinary a ofsilylmetal an aroylsilaneoxidizing with reagentsanwas acyl achieved halide often afforded byleads using to anthethe elaboratecorresponding corresponding two-step acylsila aldehy routenes, indes goodbut [5]. the yieldsThe yields first (Equation were successful usually (1)) [22synthesis low], while due ittoof is thean not aroylsilaneundesiredapplicable secondarywas for the achieved synthesis reactions by ofusing alkanoylsilanes.[22,23]. an elaborateThe oxidation two-step of α route-silyl inalcohols good yieldsusing (Equationordinary oxidizing(1)) [22], whilereagents it is oftennot applicable leads to forthe the corresponding synthesis of alkanoylsilanes. aldehydes [5]. The first successful synthesis of an aroylsilane was achieved by using an elaborate two-step route in good yields (Equation (1)) [22], while it is not applicable for the synthesis of alkanoylsilanes. (1)(1)

The dithiane route applicable for the synthesis of a wider range of acylsilanes was studied(1) by The dithiane route applicable for the synthesis of a wider range of acylsilanes was studied by Brook et al. [24] and Corey et al. [25] at the same time in 1967 (Equation (2)). The defect of the method Brook et al. [24] and Corey et al. [25] at the same time in 1967 (Equation (2)). The defect of the method is theThe use dithianeof a toxic route mercury applicable compound for the for synthesisthe hydrolysis of a wider of the rangesilylated of acylsilanesdithianes. was studied by Brookis the et use al. of [24] a toxic and Corey mercury et al. compound [25] at the for same the hydrolysistime in 1967 of (Equation the silylated (2)). dithianes. The defect of the method is the use of a toxic mercury compound for the hydrolysis of the silylated dithianes. (2)

A variety of acylsilanes have been synthesized up to date using different methods, the reactions(2)(2) of protected aldehydes, esters, and other carboxylic acid derivatives, etc. with various silicon reagents [1–9].A variety of acylsilanes have been synthesized up to date using different methods, the reactions of protectedDuring aldehydes,the course esters,of our and studies other of carboxylic the reaction acids derivatives,of an isolable etc. dialkylsilylenewith various silicon with reagentsvarious functional[1–9]. groups [26–30], we have found that the silylene inserts exclusively into the C–Cl bond of During the course of our studies of the reactions of an isolable dialkylsilylene with various MoleculesfunctionalMolecules 20162016 groups, 21, 21, 1376;, 1376; [26–30], doi:10.3390/molecules21101376 doi:10.3390/molecules21101376 we have found that the silylene inserts exclusivelywww.mdpi.com/journal/moleculeswww.mdpi.com/journal/molecules into the C–Cl bond of

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A variety of acylsilanes have been synthesized up to date using different methods, the reactions of protected aldehydes, esters, and other carboxylic acid derivatives, etc. with various silicon reagents [1–9]. During the course of our studies of the reactions of an isolable dialkylsilylene with various functional groups [26–30], we have found that the silylene inserts exclusively into the C–Cl bond Molecules 2016, 21, 1376 2 of 9 of aroyl chlorides providing rather exceptional aroyl(chloro)silanes that cannot be obtained via aroylMoleculesconventional chlorides 2016, 21, methods.1376 providing Very rather recently, exceptional an acyl(halo)silane aroyl(chloro)silanes was utilized that cannot to synthesize be obtained an isolable 2 viaof 9 conventionalsilenyllithium methods. (Equation Very (3)) [recently,31]. an acyl(halo)silane was utilized to synthesize an isolable silenyllithiumaroyl chlorides (Equ providingation (3)) rather[31]. exceptional aroyl(chloro)silanes that cannot be obtained via conventional methods. Very recently, an acyl(halo)silane was utilized to synthesize an isolable silenyllithium (Equation (3)) [31]. (3)(3)

(3) 2.2. Results Results and and Discussion Discussion

2.1. Synthesis and Characterization 2.1.2. Results Synthesis and and Discussion Characterization TheThe 1:1 1:1 reactions reactions of dialkylsilylene of dialkylsilylene 1 [32–37]1 [32 with–37 ]benzoyl with benzoyland 4-substituted and 4-substituted benzoyl chlorides benzoyl 2.1. Synthesis and Characterization− ◦ 2achlorides–2c at −302a °C–2c affordedat 30 theC correspondi afforded theng benzoyl(chloro)silanes corresponding benzoyl(chloro)silanes 3a–3c in high yields,3a– 3cindicatingin high thatyields, theThe C(carbonyl)–Cl indicating1:1 reactions that of bond thedialkylsilylene C(carbonyl)–Cl is much more 1 [32–37] reactive bond with is than much benzoyl the more carbonyl and reactive 4- substitutedgroup than (Equation the benzoyl carbonyl (4)) chlorides [38]. group No significant2a(Equation–2c at −30 difference (4)) °C [ 38afforded]. No was signiﬁcant theobserved correspondi difference in theng reactivity benzoyl(chloro)silanes was observed among inbenzoyl the reactivity 3achlorides–3c in among high 2a– 2cyields, benzoyl. Even indicating when chlorides an excessthat2a– 2cthe .amount C(carbonyl)–Cl Even whenof 1 was an bond excessused is tomuch amount a benzoyl more of reactive1 chloridewas used than (2:1 tothe mol a carbonyl benzoyl ratio), group chloridethe corresponding (Equation (2:1 mol (4)) ratio), benzoyl[38]. No the (chloro)silanesignificantcorresponding difference was benzoyl(chloro)silane obtained was observed solely as in the the was product. reactivity obtained The among solely expected asbenzoyl the reactions product. chlorides of 3 The with 2a– expected2c silylene. Even when1 reactions would an beexcessof prohibited3 with amount silylene due of to1 wouldthewas steric used be effectsprohibited to a benzoylof bulky due chloridesilylene to the steric moiety(2:1 effectsmol of ratio),3. of The bulky reactionsthe silylenecorresponding of moiety1 with alkanoyl ofbenzoyl3. The chlorides(chloro)silanereactions like of 1 acetylwaswith obtained alkanoylchloride solely and chlorides butanoylas the like product. chlori acetylde The chloride afforded expected and complex butanoylreactions reaction of chloride 3 with mixtures. affordedsilylene 1 Because complex would simplebereaction prohibited alkanoyl mixtures. due chlorides to Becausethe steric are simple effectsmore alkanoylofreactive bulky chloridesthansilylene aroyl moiety are chlorides, more of 3. reactive The the reactions pr thanoducts aroyl of of 1 withthe chlorides, reactionsalkanoyl the betweenchloridesproducts 1 like ofand the acetyl the reactions alkanoyl chloride between chlorides and butanoyl1 andmaythe react chlori alkanoyl furtherde afforded chlorideswith 1 complexto maygive the react reaction unidentified further mixtures. with products.1 to Because give the simpleunidentiﬁed alkanoyl products. chlorides are more reactive than aroyl chlorides, the products of the reactions between 1 and the alkanoyl chlorides may react further with 1 to give the unidentified products.

(4)

(4) (4) Benzoylsilanes 3a–3c, which are stable thermally with definite melting points and under moist air, were characterized by 1H-, 13C-, and 29Si-NMR spectroscopy, high-resolution mass spectrometry (HRMS),Benzoylsilanes and X-ray structure3a–3c, which analyses. are stable thermally with definite melting points and under moist Benzoylsilanes 3a–3c, which are stable thermally with definite melting points and under moist air, were characterized by 1H-, 13C-, and 29Si-NMR spectroscopy, high-resolution mass spectrometry air, were characterized by 1H-, 13C-, and 29Si-NMR spectroscopy, high-resolution mass spectrometry 2.2.(HRMS), NMR andSpectroscopy X-ray structure analyses. (HRMS), and X-ray structure analyses. In the 1H-NMR spectra of 3a–3c, two singlet signals due to four trimethylsilyl groups were 2.2. NMR Spectroscopy observed2.2. NMR in Spectroscopy the region of 0.1–0.3 ppm [0.16, 0.30 (3a); 0.17, 0.29 (3b); 0.17, 0.29 (3c)], indicating that 1 thereIn Inare the the two H-NMR1 H-NMRtypes of spectra spectratrimethylsilyl of of 3a3a––3c 3cgroups, ,two two singletbecause singlet signals signals of their due due Cs tosymmetry to four four trimethylsilyl trimethylsilyl of 3. In accord groups groups with were were the observation,observedobserved in in thetwo the region regionTMS carbon of of 0.1–0.3 0.1–0.3 (δ ca. ppm ppm 3.2 [0.16,and [0.16, 4.3 0.30 0.30 ppm) (3a (3a );and); 0.17, 0.17, silicon 0.29 0.29 signals(3b (3b);); 0.17, 0.17, (δ ca.0.29 0.29 2.8 ((3c and3c)],)], indicating5.5 indicating ppm) were that that 13 29 observedtherethere are are intwo two the types typesC- andof of trimethylsilyl trimethylsilylSi-NMR spectra groups groups of 3a because because–3c. The of of signals their their C Catss 225.3symmetry symmetry (3a), 224.5of of 33. .(In3b In accord), accord and 224.8 with with (the3c the) 13 ppmobservation,observation, in C-NMR two two spectraTMS TMS carbon carbon are ascribed (δ (δ ca.ca. 3.2 3.2to and the and carbonyl4.3 4.3 ppm) ppm) carbonand and silicon silicon signals, signals signals which (δ (δ areca.ca. 2.8at 2.8 higher and and 5.5 5.5 field ppm) ppm) relative were were 13 29 toobservedobserved the typical in in the theacylsilanes 13C-C- and and (ca.29Si-NMRSi-NMR 240 ppm) spectra spectra [39,40]. of of 3a 3aHowe–3c–3c. The.ver, The signals these signals chemicalat at 225.3 225.3 ( 3ashift (3a),), 224.5 values 224.5 (3b (3b are),), and significantly and 224.8 224.8 (3c (3c) ) 13 lowerppmppm in inthan 13C-NMRC-NMR those forspectra spectra typical are are ketones ascribed ascribed like to to thebenzophene the carbonyl carbonyl carbon(δ carbon 196.7) signals, signals,and acetophenone which which are are at at (higherδ higher 198.2), field field indicating relative relative 29 thetoto the theunique typical typical electronic acylsilanes acylsilanes feature (ca. (ca. 240of 240 acylsilanes. ppm) ppm) [39,40]. [39, 40The]. Howe However,Si-NMRver, these resonances these chemical chemical due shift shift to the values values ring are silicon are significantly significantly of 3a–3c appearlowerlower than thanat the those those same for for chemical typical typical ketones shifts ketones of like like27.8 benzophene benzopheneppm. (δ (δ 196.7)196.7) and and acetophenone acetophenone (δ (δ 198.2),198.2), indicating indicating the unique electronic feature of acylsilanes. The 29Si-NMR resonances due to the ring silicon of 3a–3c 2.3.appear Molecular at the sameStructure chemical Analysis shifts of 27.8 ppm. Molecular structures of compounds 3a–3c were determined by X-ray single-crystal diffraction 2.3. Molecular Structure Analysis analysis. Yellow single crystals of 3a–3c suitable for X-ray crystallography were obtained by slowly evaporatingMolecular the structuressolvent from of theircompounds hexane solutions.3a–3c were The determined ORTEP drawing by X-ray of compoundsingle-crystal 3a isdi depictedffraction inanalysis. Figure Yellow 1. Compound single crystals 3a was of 3acrystallized–3c suitable in for space X-ray group crystallography P-1 with twowere crystallographically obtained by slowly independentevaporating the molecules solvent fromin an their asymmetric hexane solutions.unit. The Thestructural ORTEP parameters drawing of of compound the two molecules 3a is depicted in a unitin Figure cell are 1. similarCompound but different3a was crystallizedin the torsion in anglesspace ofgroup C(1)Si(1)C(17)O(1) P-1 with two crystallographicallyand its equivalent, C(24)Si(6)C(40)O(2),independent molecules (129.03° in an and asymmetric 5.26°, respectively). unit. The structural The sum of parameters bond angles of aroundthe two C(17) molecules and C(40) in a areunit 360°, cell beingare similar in accord but withdifferent the sp in2 characterthe torsion of theangles carbonyl of C(1)Si(1)C(17)O(1) carbon atom. The and distances its equivalent, of Si(1)– C(24)Si(6)C(40)O(2), (129.03° and 5.26°, respectively). The sum of bond angles around C(17) and C(40) are 360°, being in accord with the sp2 character of the carbonyl carbon atom. The distances of Si(1)–

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the unique electronic feature of acylsilanes. The 29Si-NMR resonances due to the ring silicon of 3a–3c appear at the same chemical shifts of 27.8 ppm.

2.3. Molecular Structure Analysis Molecular structures of compounds 3a–3c were determined by X-ray single-crystal diffraction analysis. Yellow single crystals of 3a–3c suitable for X-ray crystallography were obtained by slowly evaporating the solvent from their hexane solutions. The ORTEP drawing of compound 3a is depicted in Figure1. Compound 3a was crystallized in space group P-1 with two crystallographically independent molecules in an asymmetric unit. The structural parameters of the two molecules in a unit cell are similar but different in the torsion angles of C(1)Si(1)C(17)O(1) and its equivalent, ◦ ◦ MoleculesC(24)Si(6)C(40)O(2), 2016, 21, 1376 (129.03 and 5.26 , respectively). The sum of bond angles around C(17) and 3 of 9 C(40) are 360◦, being in accord with the sp2 character of the carbonyl carbon atom. The distances of C(17)Si(1)–C(17) (1.935(3) (1.935(3)Å) and Si(6)–C(40) Å) and Si(6)–C(40) bonds bonds(1.929(2) (1.929(2) Å), are Å), significantly are signiﬁcantly larger larger than than the the normal normal Si–C bondSi–C length bond (1.87–1.89 length (1.87–1.89 Å). A similarly Å). A similarly long distance long distance of the of Si–C(carbonyl) the Si–C(carbonyl) bond bond (1.926 (1.926 Å) Å) has has been observedbeen observedin the molecular in the molecular structure structure of acetyltriphenylsilane of acetyltriphenylsilane by Trotter by Trotter et al. et [41]. al. [ 41The]. Theorigin origin may be ascribedmay beto ascribedthe effective to the σ effective(SiC)–nσ(O)(SiC)– conjugationn(O) conjugation as proposed as proposed by Ramsey, by Ramsey, Brook, Brook, Bassindale, Bassindale, and and Bock [42]. In other words, it is suggested that resonance form B contributed signiﬁcantly to the Bock [42]. In other words, it is suggested that resonance form B contributed significantly to the bonding in acylsilanes. bonding in acylsilanes.

FigureFigure 1. ORTEP 1. ORTEP drawing drawing of ofthe the independent independent moleculesin in3a 3a.. (Hydrogen (Hydrogen atoms atoms are are omitted omitted for for clarity.clarity. Thermal Thermal ellipsoids ellipsoids are areshown shown at atthe the 30% 30% pr probabilityobability level.) level.) Selected Selected bond bond lengths lengths (Å) (Å) and anglesand (°): angles Si(1)–C(4) (◦): Si(1)–C(4) 1.877(2), Si(1)–C(1) 1.877(2), Si(1)–C(1) 1.890(2), 1.890(2),Si(1)–C(17) Si(1)–C(17) 1.935(3), 1.935(3), Si(1)–Cl(1) Si(1)–Cl(1) 2.1006(9), 2.1006(9), O(1)–C(17) 1.223(3),O(1)–C(17) Si(6)–C(24) 1.223(3), 1.882(2), Si(6)–C(24) Si(6)–C(27) 1.882(2), 1.889(2), Si(6)–C(27) Si(6)–C(40) 1.889(2), Si(6)–C(40) 1.929(2), Si(6)–Cl(2) 1.929(2), Si(6)–Cl(2) 2.1001(9), 2.1001(9), O(2)–C(40) 1.227(3);O(2)–C(40) C(4)–Si(1)–C(1) 1.227(3); C(4)–Si(1)–C(1) 102.55(11), C(17)–Si(1)–Cl(1) 102.55(11), C(17)–Si(1)–Cl(1) 95.66(9), O(1)–C(17)–C(18) 95.66(9), O(1)–C(17)–C(18) 120.2(2), 120.2(2),O(1)–C(17)– Si(1)O(1)–C(17)–Si(1) 114.54(19), C(18)–C(17)–Si(1) 114.54(19), C(18)–C(17)–Si(1) 125.21(17), 125.21(17),C(24)–Si(6)–C(27) C(24)–Si(6)–C(27) 102.25(11), 102.25(11), C(40)–Si(6)–Cl(2) C(40)–Si(6)–Cl(2) 96.14(8), O(2)–C(40)–C(41)96.14(8), O(2)–C(40)–C(41) 119.4(2), O(2)–C(40)–Si(6) 119.4(2), O(2)–C(40)–Si(6) 114.64(18), 114.64(18), C(41)–C(40)–Si(6) C(41)–C(40)–Si(6) 125.89(17). 125.89(17).

Similarly,Similarly, compounds compounds 3b3b andand 3c3c werewere crystallized inin space space group groupP21/n P21/nand andP-1 P-1and and their their molecularmolecular structures structures are are shown shown in in Figures Figures 2 andand3 .3. A A single single crystal crystal of of3b 3bhas has two two crystallographically crystallographically independent molecules in the asymmetric unit, while that of 3c has one independent molecule. Their independent molecules in the asymmetric unit, while that of 3c has one independent molecule. Their structural parameters are similar to those of 3a. structural parameters are similar to those of 3a.

Figure 2. ORTEP drawing of the independent molecules in 3b. (Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 30% probability level.) Selected bond lengths (Å) and angles (°): Si(1)–C(1) 1.883(4), Si(1)–C(4) 1.898(4), Si(1)–C(17) 1.940(4), Si(1)–Cl(1) 2.1003(14), C(17)– O(1) 1.223(5), Si(6)–C(28) 1.888(4), Si(6)–C(25) 1.887(4), Si(6)–C(41) 1.927(4), Si(6)–Cl(2) 2.0967(15), C(41)–O(2) 1.216(5); C(1)–Si(1)–C(4) 102.26(17), C(17)–Si(1)–Cl(1) 97.97(13), O(1)–C(17)–C(18) 119.7(4), O(1)–C(17)–Si(1) 113.2(3), C(18)–C(17)–Si(1) 126.9(3), C(28)–Si(6)–C(25) 102.12(16), C(41)–Si(6)–Cl(2) 98.33(14), O(2)–C(41)–C(42) 119.1(4), O(2)–C(41)–Si(6) 114.4(3), C(42)–C(41)–Si(6) 126.3(3).

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C(17) (1.935(3) Å) and Si(6)–C(40) bonds (1.929(2) Å), are significantly larger than the normal Si–C bond length (1.87–1.89 Å). A similarly long distance of the Si–C(carbonyl) bond (1.926 Å) has been observed in the molecular structure of acetyltriphenylsilane by Trotter et al. [41]. The origin may be ascribed to the effective σ(SiC)–n(O) conjugation as proposed by Ramsey, Brook, Bassindale, and Bock [42]. In other words, it is suggested that resonance form B contributed significantly to the bonding in acylsilanes.

Figure 1. ORTEP drawing of the independent molecules in 3a. (Hydrogen atoms are omitted for clarity. Thermal ellipsoids are shown at the 30% probability level.) Selected bond lengths (Å) and angles (°): Si(1)–C(4) 1.877(2), Si(1)–C(1) 1.890(2), Si(1)–C(17) 1.935(3), Si(1)–Cl(1) 2.1006(9), O(1)–C(17) 1.223(3), Si(6)–C(24) 1.882(2), Si(6)–C(27) 1.889(2), Si(6)–C(40) 1.929(2), Si(6)–Cl(2) 2.1001(9), O(2)–C(40) 1.227(3); C(4)–Si(1)–C(1) 102.55(11), C(17)–Si(1)–Cl(1) 95.66(9), O(1)–C(17)–C(18) 120.2(2), O(1)–C(17)– Si(1) 114.54(19), C(18)–C(17)–Si(1) 125.21(17), C(24)–Si(6)–C(27) 102.25(11), C(40)–Si(6)–Cl(2) 96.14(8), O(2)–C(40)–C(41) 119.4(2), O(2)–C(40)–Si(6) 114.64(18), C(41)–C(40)–Si(6) 125.89(17).

Similarly, compounds 3b and 3c were crystallized in space group P21/n and P-1 and their molecular structures are shown in Figures 2 and 3. A single crystal of 3b has two crystallographically independentMolecules 2016 molecules, 21, 1376 in the asymmetric unit, while that of 3c has one independent molecule.4 of 10 Their structural parameters are similar to those of 3a.

FigureFigure 2. ORTEP 2. ORTEP drawing drawing of ofthe the independent independent molecules inin3b 3b.. (Hydrogen (Hydrogen atoms atoms are are omitted omitted for for clarity.clarity. Thermal Thermal ellipsoids ellipsoids are areshown shown at the at the 30% 30% probability probability level.) level.) Selected Selected bond bond lengths lengths (Å) (Å) and anglesand (°): angles Si(1)–C(1) (◦): Si(1)–C(1) 1.883(4), 1.883(4), Si(1)–C(4) Si(1)–C(4) 1.898(4), 1.898(4), Si(1)–C(17) Si(1)–C(17) 1.940(4), 1.940(4), Si(1)–Cl(1) Si(1)–Cl(1) 2.1003(14), 2.1003(14), C(17)– O(1) C(17)–O(1)1.223(5), Si(6)–C(28) 1.223(5), Si(6)–C(28) 1.888(4), 1.888(4), Si(6)–C(25) Si(6)–C(25) 1.887(4), 1.887(4), Si(6)–C(41) Si(6)–C(41) 1.927(4), Si(6)–Cl(2) Si(6)–Cl(2) 2.0967(15), 2.0967(15), C(41)–O(2)C(41)–O(2) 1.216(5); 1.216(5); C(1)–Si(1)–C(4) C(1)–Si(1)–C(4) 102.26(17), 102.26(17), C(17) C(17)–Si(1)–Cl(1)–Si(1)–Cl(1) 97.97(13), 97.97(13), O(1)–C(17)–C(18) O(1)–C(17)–C(18) 119.7(4), 119.7(4), O(1)–C(17)–Si(1)O(1)–C(17)–Si(1) 113.2(3), 113.2(3), C(18)–C(17)–Si(1) C(18)–C(17)–Si(1) 126.9(3), 126.9(3), C(28)–Si(6)–C(25)C(28)–Si(6)–C(25) 102.12(16), 102.12(16), C(41)–Si(6)–Cl(2) C(41)–Si(6)–Cl(2) Molecules98.33(14), 201698.33(14),, 21 O(2)–C(41)–C(42), 1376 O(2)–C(41)–C(42) 119.1(4), 119.1(4), O(2)–C(41)–Si(6) O(2)–C(41)–Si(6) 114.4(3),114.4(3), C(42)–C(41)–Si(6) C(42)–C(41)–Si(6) 126.3(3). 126.3(3). 4 of 9

FigureFigure 3. ORTEP 3. ORTEP drawing drawing of ofcompound compound 3c3c.. (Hydrogen (Hydrogen atomsatoms are are omitted omitted for for clarity. clarity. Thermal Thermal ellipsoidsellipsoids are shown are shown at the at the 30% 30% probability probability level.) level.) Sele Selectedcted bond bond lengths lengths (Å) (Å) and and angles angles (◦): (°): Si(1)–C(1) Si(1)–C(1) 1.8789(17),1.8789(17), Si(1)–C(4) Si(1)–C(4) 1.8850(16), 1.8850(16), Si(1)–C(17) Si(1)–C(17) 1.9364( 1.9364(19),19), Si(1)–Cl(1)Si(1)–Cl(1) 2.1029(7), 2.1029(7), C(17)–O(1) C(17)–O(1) 1.217(2); 1.217(2); C(1)–Si(1)–C(4)C(1)–Si(1)–C(4) 102.20(7), 102.20(7), C(17)–Si(1)–Cl(1) C(17)–Si(1)–Cl(1) 7.03(6) 7.03(6),, O(1)–C(17)–C(18)O(1)–C(17)–C(18) 18.54(16), 18.54(16), O(1)–C(17)–Si(1) O(1)–C(17)–Si(1) 15.19(14),15.19(14), C(18)–C(17)–Si(1) C(18)–C(17)–Si(1) 126.03(13). 126.03(13).

2.4. Mechanistic2.4. Mechanistic Aspects Aspects BecauseBecause the theinsertion insertion of ofsilylene silylene 1 1intointo C–Cl C–Cl [43–48] [43–48] andand Si–Cl Si–Cl [ 48[48–53]–53] bonds bonds have have been been reported, reported, it wouldit would be bedesirable desirable to proposepropose the the mechanisms mechanisms of the presentof the acylsilanepresent acylsilane formation as formation being consistent as being with the features of these precedents. The reactions of isolable dialkylsilylene 1 with chloroalkanes consistent with the features of these precedents. The reactions of isolable dialkylsilylene 1 with afford rather unusual product mixtures depending on the substrates. For example, 1 reacts with chloroalkanes afford rather unusual product mixtures depending on the substrates. For example, 1 1-chlorobutane to afford solely the corresponding butylchlorosilane 4, while the reaction of 1 with reacts with 1-chlorobutane to afford solely the corresponding butylchlorosilane 4, while the reaction CCl4 gives only dichlorosilane 5 (Equation (5)) [43]. When cyclopropylmethyl chloride is used as a of 1 substrate,with CCl4 the gives rather only unusual dichlorosilane 2:1 adduct 65 was(Equation obtained (5)) in addition[43]. When to 5 (Equationcyclopropylmethyl (6)) [43]. chloride is used as a substrate, the rather unusual 2:1 adduct 6 was obtained in addition to 5 (Equation (6)) [43].

(5)

(6)

The diverse modes of the reactions between 1 with chloroalkanes [43] suggest a complex nature of the mechanisms. The reactions may be understood uniformly starting from initially formed Lewis acid-base complexes as shown in Scheme 1. From the complex, ionic cleavage of the C–Cl bond followed by recombination would yield an alkylchlorosilane such as 4 [43]. The ionic mechanism is also applicable for the reaction of 1 with cyclopropylmethyl chloride, in which the intermediary cyclopropylmethyl cation or its equivalent 3-butenyl cation reacts with an extra silylene 1 forming 3- butenylsilyl cation and then finally 6; the 3-butenylsilyl cation would be stabilized by the coordination of the terminal π bond. Chloroalkanes with less electron donating substituents like CHCl3 and CCl4 destabilize the carbocation intermediates and instead yield 5 after the homolysis of the C–Cl bond [54]. The aroylation of 1 may occur concertedly from the acylsilane-silylene complex as shown in Equation (7). Alternatively, the facile heterolysis of the C(carbonyl)–Cl bond from the complex followed by the coupling in cage may occur exclusively; the silylene serves as a Lewis acid to activate the C(carbonyl)–Cl bond (Equation (7)). The former concerted mechanism is preferred to the latter because of the similarity of the reactions with those of chlorislanes with 1 [50,51].

Molecules 2016, 21, 1376 4 of 9 Molecules 2016, 21, 1376 4 of 9

Figure 3. ORTEP drawing of compound 3c. (Hydrogen atoms are omitted for clarity. Thermal Figureellipsoids 3. areORTEP shown drawing at the 30% of compoundprobability level.)3c. (Hydrogen Selected bondatoms lengths are omitted (Å) and for angles clarity. (°): Si(1)–C(1)Thermal ellipsoids1.8789(17), are Si(1)–C(4) shown at 1.8850(16),the 30% probability Si(1)–C(17) level.) 1.9364( Sele19),cted Si(1)–Cl(1)bond lengths 2.1029(7), (Å) and anglesC(17)–O(1) (°): Si(1)–C(1) 1.217(2); 1.8789(17),C(1)–Si(1)–C(4) Si(1)–C(4) 102.20(7), 1.8850(16), C(17)–Si(1)–Cl(1) Si(1)–C(17) 7.03(6)1.9364(, 19),O(1)–C(17)–C(18) Si(1)–Cl(1) 2.1029(7), 18.54(16), C(17)–O(1) O(1)–C(17)–Si(1) 1.217(2); C(1)–Si(1)–C(4)15.19(14), C(18)–C(17)–Si(1) 102.20(7), C(17)–Si(1)–Cl(1) 126.03(13). 7.03(6), O(1)–C(17)–C(18) 18.54(16), O(1)–C(17)–Si(1) 15.19(14), C(18)–C(17)–Si(1) 126.03(13). 2.4. Mechanistic Aspects 2.4. Mechanistic Aspects Because the insertion of silylene 1 into C–Cl [43–48] and Si–Cl [48–53] bonds have been reported, it wouldBecause be thedesirable insertion to ofpropose silylene the 1 into mechanisms C–Cl [43–48] of andthe Si–Clpresent [48–53] acylsilane bonds haveformation been reported,as being itconsistent would be with desirable the features to propose of these the precedenmechanismsts. The of reactionsthe present of acylsilaneisolable dialkylsilylene formation as 1being with consistentchloroalkanesMolecules 2016 with, 21 ,afford 1376the features rather unusual of these product preceden mixtts. uresThe dependingreactions of on isolable the substrates. dialkylsilylene For example, 1 5with of 101 chloroalkanesreacts with 1-chlorobutane afford rather tounusual afford solelyproduct the mixt correspondingures depending butylchlorosilan on the substrates.e 4, while For theexample, reaction 1 reactsof 1 with with CCl 1-chlorobutane4 gives only dichlorosilaneto afford solely 5 the(Equation corresponding (5)) [43]. butylchlorosilan When cyclopropylmethyle 4, while the chloride reaction is ofused 1 with as a CClsubstrate,4 gives the only rather dichlorosilane unusual 2:1 5 adduct(Equation 6 was (5)) obtained [43]. When in addition cyclopropylmethyl to 5 (Equation chloride (6)) [43]. is used as a substrate, the rather unusual 2:1 adduct 6 was obtained in addition to 5 (Equation (6)) [43].

(5)(5) (5)

(6) (6)(6)

The diverse modes of the reactions between 1 with chloroalkanes [43] suggest a complex nature Moleculesof the 2016TheThe mechanisms., 21diverse diverse, 1376 modes modes The ofreactions of the the reactions reactions may be between between understood 11 withwith uniformly chloroalkanes chloroalkanes starting [43] [43 from] suggest suggest initially a a complex complex formed nature natureLewis 5 of 9 ofacid-baseof the the mechanisms. mechanisms. complexes The The as reactions reactionsshown in may may Scheme be be understood understood 1. From the uniformly uniformly complex, starting starting ionic fromcleavage from initially initially of the formed formed C–Cl Lewis Lewisbond acid-basefollowed bycomplexes recombination as shown would in Schemeyield an 1.alkylchlorosilane From the complex, such ionicas 4 [43].cleavage The ionicof the mechanism C–Cl bond is acid-base complexes as shown in Scheme1. From the complex, ionic cleavage of the C–Cl bond followedalsofollowed applicable by by recombination recombination for the reaction would would of yield yield1 with an an cyclopropylmethylalkylchlorosilane alkylchlorosilane such suchchloride, as as 4 4[43]. [in43 which].The The ionic ionicthe mechanism intermediary mechanism is alsocyclopropylmethylis also applicable applicable for for cationthe the reaction reactionor its equivalentof of 1 1withwith 3-bucyclopropylmethyl cyclopropylmethyltenyl cation reacts chloride, chloride, with an in inextra which which silylene the the intermediary intermediary 1 forming 3- cyclopropylmethylbutenylsilylcyclopropylmethyl cation cation cationand orthen or its its equivalentfinally equivalent 6; 3-buthe 3-butenyl tenyl3-butenylsilyl cation cation reactsreacts cation with with would an an extra extra be silylene silylenestabilized 1 forming1 formingby the 3- (7) butenylsilylcoordination3-butenylsilyl cationof cation the andterminal thenthen ﬁnallyπ finallybond.6;the Chloroalkanes6; 3-butenylsilylthe 3-butenylsilyl with cation less wouldcation electron bewould stabilized donating be bystabilized substituents the coordination by likethe coordination of the terminal π bond. Chloroalkanes with less electron donating substituents like CHClof the3 terminaland CCl4π destabilizebond. Chloroalkanes the carbocation with intermediates less electron donating and instead substituents yield 5 after like the CHCl homolysis3 and CCl of4 CHClthedestabilize C–Cl3 and bond theCCl carbocation[54].4 destabilize intermediates the carbocation and intermediates instead yield 5andafter instead the homolysis yield 5 after ofthe the C–Cl homolysis bond [54 of]. the C–ClThe bondaroylation [54]. of 1 may occur concertedly from the acylsilane-silylene complex as shown in EquationThe aroylation(7). Alternatively, of 1 may the occur facile concertedly heterolysis from of the acylC(carbonyl)–Clsilane-silylene bond complex from asthe shown complex in Equationfollowed by(7). the Alternatively, coupling in cage the mayfacile occur heterolysis exclusively; of the the C(carbonyl)–Cl silylene serves asbond a Lewis from acid the to complex activate followedthe C(carbonyl)–Cl by the coupling bond in(Equation cage may (7)). occur The exclusively; former concerted the silylene mechanism serves as is a preferredLewis acid to to the activate latter thebecause C(carbonyl)–Cl of the similarity bond of(Equation the reactions (7)). Thewith former those of concerted chlorislanes mechanism with 1 [50,51]. is preferred to the latter because of the similarity of the reactions with those of chlorislanes with 1 [50,51].

SchemeScheme 1. 1.MechanismsMechanisms of of the the reactions of of1 1with with chloroalkanes. chloroalkanes.

The Theinsertion aroylation reactions of 1 may of silylene occur concertedly 1 into the from Si–Cl the bonds acylsilane-silylene of chlorosilanes complex have as been shown found in to occurEquation cleanly [49,50]; (7). Alternatively, hence, the theconcerted facile heterolysis mechanism of via the three-membered C(carbonyl)–Cl bond cyclic from transition the complex states has beenfollowed proposed. by theThe coupling mechanism in cage has may been occur supported exclusively; by thethesilylene detailed serves DFT as calculations a Lewis acid [55–57]. to activate the C(carbonyl)–Cl bond (Equation (7)). The former concerted mechanism is preferred to the latter

because of the similarity of the reactions with those of chlorislanes with 1 [50,51]. Molecules 2016, 21, 1376 5 of 9 (8)

3. Materials and Methods (7)(7) 3.1. General Procedures Manipulation of air-sensitive compounds was performed under a controlled dry argon atmosphere using standard Schlenk techniques. Tetrahydrofuran (THF), hexane, and toluene were distilled from sodium–benzophenone. All the other reagents were obtained from commercial suppliers and used without further purification. Dialkylsilylene 1 was prepared according to literature procedures [32]. 1H- (400 MHz), 13C- (100.6 MHz), and 29Si- (79.5 MHz) NMR spectra were recorded on a Bruker AV- 400 spectrometer at room temperature (Bruker, Rheinstetten, Germany), using CDCl3 as the solvent. Melting points are uncorrected. High-resolution mass spectra (HRMS) were recorded on a Bruker Daltonics Apex-III spectrometer (Bruker, Rheinstetten, Germany).

3.2. Synthesis

3.2.1. Synthesis of 3a Scheme 1. Mechanisms of the reactions of 1 with chloroalkanes. A hexane solution of benzoyl chloride (0.45 g, 3.2 mmol) was added to a solution of The insertion reactions of silylene 1 into the Si–Cl bonds of chlorosilanes have been found to dialkylsilyleneoccur cleanly 1 (1.12[49,50]; g, hence,3.0 mmol) the concerted in hexane mechanis at −30 m°C. via The three-membered reaction mixture cyclic was transition allowed states to hasstir for 2 h atbeen 0 °C. proposed. The color The of mechanism the solution has beenchanged supported from byred the to detailed yellow. DFT Then, calculations the solvent [55–57]. was removed under vacuum. The resulting residue was purified by flash chromatography (Silica gel, 200–300 mesh; ethyl acetate/hexane, 1:300) to yield 3a as a yellow solid. Yield: 0.98 g (64%). m.p. 152–154 °C; 1H- (8) NMR (400 MHz, CDCl3): δ 8.07 (d, J = 7.2 Hz, 2H, o-Ar), 7.56 (t, J = 7.2 Hz, 1H, p-Ar), 7.49 (t, J = 7.2 Hz,

2H, m-Ar), 2.14 (s, 4H, CH2), 0.30 (s, 18H, SiMe3), 0.16 (s, 18H, SiMe3). 13C-NMR (101 MHz, CDCl3): δ 225.28 (C=O),138.90 (CAr-C(O)),133.22 (p-Ar), 129.42 (o-Ar), 128.30 (m-Ar), 33.25 (CH2), 12.50 3. Materials and Methods (C(SiMe3)2), 4.27 (SiMe3), 3.25 (SiMe3); 29Si-NMR (80 MHz, CDCl3): δ 27.84 (SiCl), 5.53 (SiMe3), 2.85 (SiMe3.1.3); HRMS(ESI)General Procedures calculated for C23H45ClOSi5: 513.2079, found 513.2078. Manipulation of air-sensitive compounds was performed under a controlled dry argon atmosphere using standard Schlenk techniques. Tetrahydrofuran (THF), hexane, and toluene were distilled from sodium–benzophenone. All the other reagents were obtained from commercial suppliers and used without further purification. Dialkylsilylene 1 was prepared according to literature procedures [32]. 1H- (400 MHz), 13C- (100.6 MHz), and 29Si- (79.5 MHz) NMR spectra were recorded on a Bruker AV- 400 spectrometer at room temperature (Bruker, Rheinstetten, Germany), using CDCl3 as the solvent. Melting points are uncorrected. High-resolution mass spectra (HRMS) were recorded on a Bruker Daltonics Apex-III spectrometer (Bruker, Rheinstetten, Germany).

3.2. Synthesis

3.2.1. Synthesis of 3a A hexane solution of benzoyl chloride (0.45 g, 3.2 mmol) was added to a solution of dialkylsilylene 1 (1.12 g, 3.0 mmol) in hexane at −30 °C. The reaction mixture was allowed to stir for 2 h at 0 °C. The color of the solution changed from red to yellow. Then, the solvent was removed under vacuum. The resulting residue was purified by flash chromatography (Silica gel, 200–300 mesh; ethyl acetate/hexane, 1:300) to yield 3a as a yellow solid. Yield: 0.98 g (64%). m.p. 152–154 °C; 1H- NMR (400 MHz, CDCl3): δ 8.07 (d, J = 7.2 Hz, 2H, o-Ar), 7.56 (t, J = 7.2 Hz, 1H, p-Ar), 7.49 (t, J = 7.2 Hz, 2H, m-Ar), 2.14 (s, 4H, CH2), 0.30 (s, 18H, SiMe3), 0.16 (s, 18H, SiMe3). 13C-NMR (101 MHz, CDCl3): δ 225.28 (C=O),138.90 (CAr-C(O)),133.22 (p-Ar), 129.42 (o-Ar), 128.30 (m-Ar), 33.25 (CH2), 12.50 (C(SiMe3)2), 4.27 (SiMe3), 3.25 (SiMe3); 29Si-NMR (80 MHz, CDCl3): δ 27.84 (SiCl), 5.53 (SiMe3), 2.85 (SiMe3); HRMS(ESI) calculated for C23H45ClOSi5: 513.2079, found 513.2078.

Molecules 2016, 21, 1376 5 of 9

(7)

Molecules 2016, 21, 1376 6 of 10

Scheme 1. Mechanisms of the reactions of 1 with chloroalkanes. The insertion reactions of silylene 1 into the Si–Cl bonds of chlorosilanes have been found to occur cleanlyThe [49 insertion,50]; hence, reactions the concerted of silylene mechanism 1 into the via Si–Cl three-membered bonds of chlorosilanes cyclic transition have states been hasfound been to proposed.occur cleanly The [49,50]; mechanism hence, has the been concerted supported mechanis by them detailedvia three-membered DFT calculations cyclic [ 55transition–57]. states has been proposed. The mechanism has been supported by the detailed DFT calculations [55–57].

(8)(8)

3.3. Materials Materials and and Methods Methods

3.1.3.1. GeneralGeneral ProceduresProcedures ManipulationManipulation of of air-sensitive air-sensitive compounds compounds was performed was performed under a under controlled a controlled dry argon atmosphere dry argon atmosphereusing standard using Schlenk standard techniques. Schlenk Tetrahydrofuran techniques. Tetrahydrofuran (THF), hexane, (THF), and toluene hexane, were and toluenedistilled werefrom distilledsodium–benzophenone. from sodium–benzophenone. All the other All reagents the other were reagents obtained were from obtained commercial from commercial suppliers suppliersand used andwithout used further without purification. further purification. Dialkylsilylene Dialkylsilylene 1 was prepared1 wasaccording prepared to literature according procedures to literature [32]. 1 13 29 procedures1H- (400 MHz), [32]. 13C-H- (100.6 (400 MHz), MHz), andC- (100.6 29Si- (79.5 MHz), MHz) and NMRSi- (79.5 spectra MHz) were NMR recorded spectra on were a Bruker recorded AV- on a Bruker AV-400 spectrometer at room temperature (Bruker, Rheinstetten, Germany), using CDCl 400 spectrometer at room temperature (Bruker, Rheinstetten, Germany), using CDCl3 as the solvent.3 asMelting the solvent. points Melting are uncorrected. points are High-resolution uncorrected. High-resolution mass spectra mass(HRMS) spectra were (HRMS) recorded were on recordeda Bruker onDaltonics a Bruker Apex-III Daltonics spectrometer Apex-III spectrometer (Bruker, Rheinstetten, (Bruker, Rheinstetten, Germany). Germany). 3.2. Synthesis 3.2. Synthesis 3.2.1. Synthesis of 3a 3.2.1. Synthesis of 3a A hexane solution of benzoyl chloride (0.45 g, 3.2 mmol) was added to a solution of dialkylsilyleneA hexane1 solution(1.12 g, 3.0of mmol)benzoyl in hexanechloride at (0.4−305 ◦g,C. 3.2 The mmol) reaction was mixture added was to alloweda solution to stir of fordialkylsilylene 2 h at 0 ◦C. The 1 (1.12 color g, of3.0 the mmol) solution in hexane changed at − from30 °C. red The to reaction yellow. Then,mixture the was solvent allowed was removedto stir for under2 h at vacuum.0 °C. The The color resulting of the residuesolution was changed purified from by flashred to chromatography yellow. Then, the (Silica solvent gel, 200–300 was removed mesh; ethylunder acetate/hexane, vacuum. The resulting 1:300) toresidue yield was3a as purified a yellow by flash solid. chromatography Yield: 0.98 g (64%). (Silica m.p.gel, 200–300 152–154 mesh;◦C; 1ethyl acetate/hexane, 1:300) to yield 3a as a yellow solid. Yield: 0.98 g (64%). m.p. 152–154 °C; 1H- H-NMR (400 MHz, CDCl3): δ 8.07 (d, J = 7.2 Hz, 2H, o-Ar), 7.56 (t, J = 7.2 Hz, 1H, p-Ar), 7.49 NMR (400 MHz, CDCl3): δ 8.07 (d, J = 7.2 Hz, 2H, o-Ar), 7.56 (t, J = 7.2 Hz, 1H, p-Ar), 7.49 (t, 13J = 7.2 Hz, (t, J = 7.2 Hz, 2H, m-Ar), 2.14 (s, 4H, CH2), 0.30 (s, 18H, SiMe3), 0.16 (s, 18H, SiMe3). C-NMR 2H, m-Ar), 2.14 (s, 4H, CH2), 0.30 (s, 18H, SiMe3), 0.16 (s, 18H, SiMe3). 13C-NMR (101 MHz, CDCl3): δ (101 MHz, CDCl3): δ 225.28 (C=O),138.90 (CAr-C(O)),133.22 (p-Ar), 129.42 (o-Ar), 128.30 (m-Ar), 33.25 225.28 (C=O),138.90 (CAr-C(O)),133.22 (p-Ar), 129.4229 (o-Ar), 128.30 (m-Ar), 33.25 (CH2), 12.50 (CH2), 12.50 (C(SiMe3)2), 4.27 (SiMe3), 3.25 (SiMe3); Si-NMR (80 MHz, CDCl3): δ 27.84 (SiCl), 5.53 (C(SiMe3)2), 4.27 (SiMe3), 3.25 (SiMe3); 29Si-NMR (80 MHz, CDCl3): δ 27.84 (SiCl), 5.53 (SiMe3), 2.85 (SiMe3), 2.85 (SiMe3); HRMS(ESI) calculated for C23H45ClOSi5: 513.2079, found 513.2078. (SiMe3); HRMS(ESI) calculated for C23H45ClOSi5: 513.2079, found 513.2078. 3.2.2. Synthesis of 3b A hexane solution of p-methyl benzoyl chloride (0.49 g, 3.2 mmol) was added to a solution of dialkylsilylene 1 (1.12 g, 3.0 mmol) in hexane at −30 ◦C. The reaction mixture was allowed to stir for 2 h at 0 ◦C. The color of the solution changed from red to yellow. Then, the solvent was removed under vacuum. The resulting residue was purified by flash chromatography (Silica gel, 200–300 mesh; ethyl acetate/hexane, 1:300) to yield 3b as a yellow solid. Yield: 0.97 g (61%). m.p. 174–177 ◦C; 1 H-NMR (400 MHz, CDCl3): δ 7.96 (d, J = 7.2 Hz, 2H, o-Ar), 7.29 (d, J = 7.2 Hz, 2H, m-Ar), 2.43 (s, 3H, 13 Ar-Me), 2.13 (s, 4H, CH2), 0.29 (s, 18H, SiMe3), 0.17 (s, 18H, SiMe3). C-NMR (101 MHz, CDCl3): δ 224.53 (C=O), 144.13 (CAr-C(O)), 150.00, 136.63 (p-Ar), 129.59 (o-Ar), 128.98 (m-Ar), 33.24 (CH2), 21.77 29 (Ar-Me), 12.44 (C(SiMe3)2), 4.28 (SiMe3), 3.24 (SiMe3). Si-NMR (79 MHz, CDCl3): δ 27.84 (SiCl), 5.47 (SiMe3), 2.81 (SiMe3); HRMS(ESI) calculated for C24H47ClOSi5: 527.2225, found 527.2235.

3.2.3. Synthesis of 3c A hexane solution of p-trifluoromethyl benzoyl chloride (0.67 g, 3.2 mmol) was added to a solution of dialkylsilylene 1 (1.12 g, 3.0 mmol) in hexane at −30 ◦C. The reaction mixture was allowed to stir Molecules 2016, 21, 1376 7 of 10 for 2 h at 0 ◦C. The color of the solution changed from red to yellow. Then, the solvent was removed under vacuum. The resulting residue was purified by flash chromatography (Silica gel, 200–300 mesh; ethyl acetate/hexane, 1:300) to yield 3c as a yellow solid. Yield: 1.16 g, (67%). m.p. 160–163 ◦C; 1 H-NMR (400 MHz, CDCl3): δ 8.17 (d, J = 7.2 Hz, 2H, o-Ar), 7.76 (d, J = 7.2 Hz, 2H, m-Ar), 2.16 (s, 4H, 13 CH2), 0.29 (s, 18H, SiMe3), 0.17 (s, 18H, SiMe3). C-NMR (101 MHz, CDCl3): δ 224.78 (C=O), 140.87 (CAr-C(O)), 134.31 (dd, p-Ar), 129.57 (m-Ar), 124.86 (o-Ar), 123.61 (dd, JC-F = 271, CF3), 33.26 (CH2), 29 12.61 (C(SiMe3)2), 4.29 (SiMe3), 3.22 (SiMe3). Si-NMR (80 MHz, CDCl3) δ 27.83 (SiCl), 5.66 (SiMe3), 2.94 (SiMe3); HRMS(ESI) calculated for C24H44ClF3OSi5: 581.1949, found 581.1952.

3.3. X-ray Crystallography The diffraction data of 3a–3c were collected on a Bruker Smart Apex II CCD diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). All of the data were collected at ambient temperatures, and the structures were solved via the direct method and subsequently reﬁned on F2 using full-matrix least-squares techniques (SHELXTL) [58]. Absorption corrections were applied empirically using the SADABS program [59]. The non-hydrogen atoms were reﬁned anisotropically, and hydrogen atoms were located at calculated positions. A summary of the crystallographic data and selected experimental information is given in Table S1.

4. Conclusions Isolable dialkylsilylene 1 was found to react with the C(carbonyl)–Cl bonds in aroyl chlorides 2 at low temperatures highly chemoselectively to give aroyl(chloro)silanes 3; the carbonyl groups in neither 2 nor 3 react with silylene 1. The structural analysis using NMR and X-ray crystallography indicate the lower ﬁeld 13C-NMR resonance of the carbonyl carbon and longer Si–C(carbonyl) bond distance than the standard values. The facile and highly selective nature of the reactions suggests that the insertion occurs concertedly from the initial Lewis acid-base complexes, similarly to that of 1 into the Si–Cl bonds in chlorosilanes. We are hoping the present synthetic methodology is applicable in general for a wide variety of silylenes. The silylenes should be however relatively long-lived and their reactions with the aroyl chlorides should be fast enough to prevent their oligomerization. Further works on the acylsilanes with unique electronic properties are under progress in our laboratory.

Supplementary Materials: Supplementary materials can be accessed at: http://www.mdpi.com/1420-3049/21/ 10/1376/s1. Crystallographic information for compounds 3a–3c in CIF format and crystallographic tables. Acknowledgments: This work was financially supported by the National Natural Science Foundation of China (Grant No. 21472032) and the Natural Science Foundation of Zhejiang Province (Grant No. LY17B010002). Author Contributions: Z.L. conceived and designed the experiments; X.L., Q.L. and X.-Q.X. performed the experiments; X.-Q.X., X.L., Q.L., Z.L., G.L. and M.K. analyzed the data; X.-Q.X., Z.L. and M.K. wrote the paper. All authors have given approval to the final version of the manuscript. Conflicts of Interest: The authors declare no conflict of interest.

Appendix A Crystallography data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Center, CCDC 979677 (3a), 979676 (3b) and 979675 (3c). Copies of these data can be obtained free of charge on application to the Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: [email protected] or http://www.http.ccdc.cam.ac.hk).

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Sample Availability: Samples of the compounds 3a–3c are available from the authors.

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