inorganics

Article Si–H Bond Activation of a Primary with a Pt(0) Complex: Synthesis and Structures of Mononuclear (Hydrido)(dihydrosilyl) Platinum(II) Complexes

Norio Nakata * ID , Nanami Kato, Noriko Sekizawa and Akihiko Ishii *

Department of Chemistry, Graduate School of Science and Engineering, Saitama University, 255 Shimo-okubo, Sakura-ku, Saitama 338-8570, Japan; [email protected] (N.K.); [email protected] (N.S.) * Correspondence: [email protected] (N.N.); [email protected] (A.I.); Tel.: +81-48-858-3392 (N.N.); Fax: +81-48-858-3700 (N.N.)

Received: 3 October 2017; Accepted: 24 October 2017; Published: 25 October 2017

Abstract: A hydrido platinum(II) complex with a dihydrosilyl , [cis-PtH(SiH2Trip)(PPh3)2](2) was prepared by oxidative addition of an overcrowded primary silane, TripSiH3 (1, Trip = 9-triptycyl) 2 with [Pt(η -C2H4)(PPh3)2] in toluene. The ligand-exchange reactions of complex 2 with free resulted in the formation of a series of (hydrido)(dihydrosilyl) complexes (3–5). Thus, the replacement of two PPh3 ligands in 2 with a bidentate bis(phosphine) ligand such as DPPF [1,2-bis(diphenylphosphino)] or DCPE [1,2-bis(dicyclohexylphosphino)ethane] gave the corresponding complexes [PtH(SiH2Trip)(L-L)] (3: L-L = dppf, 4: L-L = dcpe). In contrast, the ligand-exchange reaction of 2 with an excess amount of PMe3 in toluene quantitatively produced [PtH(SiH2Trip)(PMe3)(PPh3)] (5), where the PMe3 ligand is adopting trans to the hydrido ligand. The structures of complexes 2–5 were fully determined on the basis of their NMR and IR spectra, and elemental analyses. Moreover, the low-temperature X-ray crystallography of 2, 3, and 5 revealed that the platinum center has a distorted square planar environment, which is probably due to the steric requirement of the cis-coordinated phosphine ligands and the bulky 9-triptycyl group on the atom.

Keywords: platinum; primary silane; hydrido complex; oxidative addition; ligand-exchange reaction; X-ray crystallography

1. Introduction The transition catalyzed synthesis of functionalized compounds gained substantial momentum during the past few decades [1]. Among these catalytic conversions, the oxidative addition of hydrosilanes with platinum(0) complexes is an efficient method for the generation of the platinum(II) species, which has been proposed as a key intermediate in platinum-catalyzed hydrosilylations [2–6] and bis-silylations [7,8], as well as the dehydrogenative couplings of hydrosilanes [9–13]. While a number of reactions of hydrosilanes with platinum(0) complexes affording mononuclear bis(silyl) [14–18] and silyl-bridged multinuclear complexes [19–29] have been described so far, the isolation of mononuclear hydrido(silyl) complexes has been less well studied due to the high reactivity of a Pt–H bond [30–34]. In particular, the synthesis of hydrido(dihydrosilyl) platinum(II) complexes, which are anticipated as the initial products in the Si–H bond activation reactions of primary with platinum(0) complexes, is quite rare. Indeed, only two publications have previously reported the characterization of hydrido(dihydrosilyl) platinum(II) complexes. In 2000, Tessier et al. reported that the reaction of a primary silane with a bulky m-terphenyl group with [Pt(PPr)3] produced the first example of a stable hydrido(dihydrosilyl) complex [cis-PtH(SiH2Ar)(PPr3)2] (Ar = 2,6-MesC6H3)[35]. Quite recently, Lai et al. also

Inorganics 2017, 5, 72; doi:10.3390/inorganics5040072 www.mdpi.com/journal/inorganics Inorganics 2017, 5, 72 2 of 11 Inorganics 2017, 5, 72 2 of 11

t described the synthesis of a bis(phosphine) hydrido(dihydrosilyl) complex [PtH(SiH2Si Bu2Me)(dcpe)] of a bis(phosphine) hydrido(dihydrosilyl) complex [PtH(SiH2SitBu2Me)(dcpe)] (dcpe = 1,2- bis(dicyclohexylphos(dcpe = 1,2-bis(dicyclohexylphosphino)ethane)phino)ethane) containing containinga Si–Si bond a Si–Si [36]. bond Meanwhile, [36]. Meanwhile, we succeeded we succeeded in the in the first isolation of a series of hydrido(dihydrogermyl) platinum(II) complexes [PtH(GeH2Trip)(L)] first isolation of a series of hydrido(dihydrogermyl) platinum(II) complexes [PtH(GeH2Trip)(L)] (Trip =(Trip 9-triptycyl) = 9-triptycyl) using using a bulky a bulky substi substituent,tuent, 9-triptycyl 9-triptycyl group group [37]. [37 In]. Inaddition, addition, we we reported reported the the first first synthesessyntheses and and structural structural characterizations characterizations of of hydrido hydrido palladium(II) palladium(II) complexes complexes with with a a dihydrosilyl- dihydrosilyl- or dihydrogermyl ligand, [PdH(EH2Trip)(dcpe)] (E = Si, Ge) [38]. Very recently, we also found that or dihydrogermyl ligand, [PdH(EH2Trip)(dcpe)] (E = Si, Ge) [38]. Very recently, we also found that hydride-abstraction reactions of [MH(EH Trip)(dcpe)] (M = Pt, Pd, E = Si, Ge) with B(C F ) led to the hydride-abstraction reactions of [MH(EH22Trip)(dcpe)] (M = Pt, Pd, E = Si, Ge) with B(C66F5)33 led to the formationsformations of of new new cationic cationic dinuclear dinuclear complexes complexes with with bridging bridging hydrogermylene hydrogermylene and and hydrido hydrido ligands, ligands, [{M(dcpe)} (µ-GeHTrip)(µ-H)]+ [39]. As an extension of our previous work and taking into account the [{M(dcpe)}22(μ-GeHTrip)(μ-H)]+ [39]. As an extension of our previous work and taking into account theinterest interest devoted devoted to hydrido to hydrido platinum(II) platinum(II) complexes, complexes, we present we here present the synthesis here andthe characterizationsynthesis and of a series of mononuclear (hydrido)(dihydrosilyl) complexes [PtH(SiH Trip)(L) ]. characterization of a series of mononuclear (hydrido)(dihydrosilyl) complexes2 [PtH(SiH2 2Trip)(L)2]. 2. Results 2. Results

2.1. Synthesis and Characterization of [cis-PtH(SiH2Trip)(PPh3)2](2) 2.1. Synthesis and Characterization of [cis-PtH(SiH2Trip)(PPh3)2] (2) 2 The reaction of TripSiH3 1 with [Pt(η -C2H4)(PPh3)2] in toluene proceeded efficiently at room The reaction of TripSiH3 1 with [Pt(η2-C2H4)(PPh3)2] in toluene proceeded efficiently at room temperature under inert atmosphere to form the corresponding complex [cis-PtH(SiH2Trip)(PPh3)2] temperature(2) in 91% yield under as inert colorless atmosphere crystals to (Scheme form the1). corresponding In the 1H NMR complex spectrum [cis-PtH(SiH of 2, the2 characteristicTrip)(PPh3)2] 1 (signals2) in 91% of yield the platinumas colorless hydride crystals were (Scheme observed 1). In the at δ H= NMR−2.15, spectrum which wereof 2, the split characteristic by 19 and 31 signals157 Hz of of the31 platinumP–1H couplings hydride accompanyingwere observed at 958 δ = Hz−2.15, of which satellite were signals split by from 19 and the 157195 PtHz isotope.of P– 1 195 ThisH couplings chemical accompanying shift is comparable 958 Hz of with satellite those signals of the from related the (hydrido)(dihydrosilyl)Pt isotope. This chemical complexes, shift is comparable with those of the related (hydrido)(dihydrosilyl) complexes, [cis-PtH(SiH2tAr)(PPr3)2] (Ar [cis-PtH(SiH2Ar)(PPr3)2](Ar = 2,6-MesC6H3) (δ = −3.40) [35] and [cis-PtH(SiH2Si Bu2Me)(dcpe)] = 2,6-MesC6H3) (δ = −3.40) [35] and [cis-PtH(SiH2SitBu2Me)(dcpe)] (δ = −0.89) [36]. The SiH31 2 resonance1 (δ = −0.89)[36]. The SiH2 resonance appeared as a multiplet at δ = 4.68 ppm. The P{ H} NMR appeared as a multiplet at δ = 4.68 ppm. 2The 31P{1H} NMR spectrum of 2 exhibited195 two doublets31 (2JP– spectrum of 2 exhibited two doublets ( JP–P = 15 Hz) at δ = 33.8 and 34.5 with Pt– P coupling 195 31 Pconstants, = 15 Hz) 2183at δ and= 33.8 1963 and Hz, 34.5 which with were Pt– assignedP coupling to the phosphorusconstants, 2183 atoms and lying 1963trans Hz,to which the hydrido were assignedand dihydrosilyl to the ligands, respectively, atoms lying intrans agreement to the hydrido with the and NMR dihydrosilyl data for ligands, reported respectively, germanium in agreement with the NMR data for reported germanium1 congener [cis-PtH(GeH1 2Trip)(PPh3)2] [δ = congener [cis-PtH(GeH2Trip)(PPh3)2][δ = 31.2 ( JPt–P = 2317 Hz) and 31.6 ( JPt–P = 2252 Hz)] [37]. 1 1 31.2The ( siliconJPt–P = 2317 atom Hz) of and2 gave 31.6 rise ( JPt–P to = a 2252 resonance Hz)] [37]. around The siliconδ = −40.6 atom with of 2 splittinggave rise dueto a toresonance31P–29Si around δ = 2−40.6 with splitting2 due to 31P–29Si couplings195 (2JP(trans)–Si =1 161, 2JP(cis)–Si = 15 Hz) and29 1951Pt couplings ( JP(trans)–Si = 161, JP(cis)–Si = 15 Hz) and Pt satellites ( JPt–Si = 1220 Hz) in the Si{ H} 1 29 1 satellitesNMR spectrum. ( JPt–Si = 1220 In theHz) solid in the state Si{ IRH} spectrum NMR spectrum. for 2, Pt–H In the and solid Si–H state stretching IR spectrum vibrations for 2, Pt–H were −1 andobserved Si–H atstretching 2041 and vibrations 2080 cm−1 were, respectively. observed Complex at 2041 2andis thermally 2080 cm and, respectively. air stable in Complex the solid state2 is thermally(: and air 123 stable◦C (dec.)) in theor insolid solution, state and(melting no dimerization point: 123 or°C dissociation (dec.)) or ofin phosphinesolution, and ligands no dimerizationwas observed. or dissociation of phosphine ligands was observed.

Scheme 1. Synthesis of [cis-PtH(SiH2Trip)(PPh3)2] 2. Scheme 1. Synthesis of [cis-PtH(SiH2Trip)(PPh3)2] 2. The molecular structure of 2 was determined unambiguously by X-ray crystallographic analysis, as depictedThe molecular in Figure structure1. The of X-ray 2 was crystallographic determined unambiguously analysis of 2 byrevealed X-ray crystallographic that the platinum analysis, center asattains depicted a distorted in Figure square-planar 1. The X-ray environment, crystallographic which analysis was probably of 2 revealed due to that the stericthe platinum requirement center of attainsthe cis-coordinated a distorted square-planar PPh3 ligands environment, and the bulky whic 9-triptycylh was probably group on due the siliconto the steric atom. requirement The P1–Pt1–P2 of theangle cis-coordinated of 101.63(3)◦ PPhand3 ligands P1–Pt1–Si1 and anglethe bulky of 96.17(3) 9-triptycyl◦ deviated group on considerably the silicon atom. from theThe ideal P1–Pt1–P2 90◦ of anglesquare-planar of 101.63(3)° geometry. and P1–Pt1–Si1 The Pt–Si bondangle length of 96.17(3)° is 2.3458(9) deviated Å, which considerably is comparable from the to those ideal ranging 90° of square-planarfrom 2.321 to geometry. 2.406 Å observed The Pt–Si in bond the relatedlength is mononuclear 2.3458(9) Å, which platinum(II) is comparable complexes to those bearing ranging silyl fromligands 2.321 [1]. to The 2.406 Å observed atom on in the the platinum related atommononuclear was located platinum(II) in the electron complexes bearing map and silyl has ligands [1]. The hydrogen atom on the platinum atom was located in the electron density map and has a Pt–H distance of 1.59(4) Å. The Pt1–P1 [2.2945(8) Å] is slightly shorter than the Pt1– P2 bond length [2.3401(8) Å], which indicates the stronger trans influence of the silicon atom

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aInorganics Pt–H distance 2017, 5, 72 of 1.59(4) Å. The Pt1–P1 bond length [2.2945(8) Å] is slightly shorter than the Pt1–P23 of 11 bond length [2.3401(8) Å], which indicates the stronger trans influence of the silicon atom compared withcompared that of with the hydridethat of the in hydride this complex. in this This complex. result This is consistent result is withconsistent the 195 withPt–31 theP coupling 195Pt–31P constantscoupling (2183constants and 1963(2183 Hz) and observed 1963 Hz) inobserved the 31P{ 1inH} the NMR 31P{1 spectrum.H} NMR spectrum.

Figure 1. 1. ORTEPORTEP of [ ofcis-PtH(SiH [cis-PtH(SiH2Trip)(PPh2Trip)(PPh3)2] 23 (50%)2] 2 thermal(50% thermal ellipsoids, ellipsoids, a solvation a solvation toluene , toluene molecule,and hydrogen and atoms, hydrogen except atoms, H1, H2, except and H1,H3 were H2, andomitted H3 werefor clarity). omitted Selected for clarity). bond lengths Selected (Å) bond and lengthsbond angles (Å) and(°): Pt1–Si1 bond angles= 2.3458(9), (◦): Pt1–P1 Pt1–Si1 = 2.2945(8), = 2.3458(9), Pt1–P2 Pt1–P1 = 2.3401(8), = 2.2945(8), Pt1–H1 Pt1–P2 = 1.59(4), = 2.3401(8), Si1–C1 = Pt1–H11.918(3), = P1–Pt1–P2 1.59(4), Si1–C1 = 101.63(3), = 1.918(3) Si1–Pt1–P1, P1–Pt1–P2 = =96.17( 101.63(3),3), Si1–Pt1–H1 Si1–Pt1–P1 = =79.7(16), 96.17(3), P2–Pt1–H1 Si1–Pt1–H1 = = 82.5(16), 79.7(16), P2–Pt1–H1Si1–Pt1–P2 = 82.5(16),162.13(3), Si1–Pt1–P2 P1–Pt1–H1 = = 162.13(3), 175.8(16). P1–Pt1–H1 = 175.8(16).

2.2. Ligand Exchange Reactions of 2 with Free Phosphine Ligands WeWe next examined examined the the ligand-exchange ligand-exchange reactions reactions of ofcomplex complex 2 with2 with free freephosphine phosphine ligands. ligands. The Thereplacement replacement of two of twoPPh3 PPh ligands3 ligands in 2 inwith2 witha bidentate a bidentate bis(phosphine) bis(phosphine) ligand ligand such suchas DPPF as DPPF (1,2- (1,2-bis(diphenylphosphino)ferrocene)bis(diphenylphosphino)ferrocene) or orDCPE DCPE gave gave the the corresponding corresponding complexes complexes [PtH(SiH [PtH(SiH22Trip)(L-L)]Trip)(L-L)] ((33:: L-LL-L == dppf,dppf, 44:: L-LL-L = = dcpe)dcpe) in in 87% 87% and and 80% 80% yields, yields, respectively respectively (Scheme (Scheme2). 2).In theIn the1H 1 NMRH NMR spectra spectra of 2 2 1 1 3ofand 3 and4, the4, the hydride hydride resonated resonated as aas doublet a doublet of doubletsof doublets at δat= δ–1.62 = –1.62( J (P–HJP–H= = 20, 20, 164, 164, JPt–HJPt–H = 995 Hz) 22 1 1 forfor 33 andand –0.46–0.46 (( JP–H == 13, 13, 166, 166, JPt–HJPt–H = 1004= 1004 Hz) Hz) for for 4. 4These. These chemical chemical shifts shifts are are shifted shifted downfield downfield in incomparison comparison with with that that of of the the starting starting complex complex 22 ((δδ == −−2.15),2.15), which which is is probably probably due due to the stronger electron-donating ability ofof chelatingchelating phosphinesphosphines comparedcompared withwith PPhPPh33.. The The spectrum for 3 alsoalso displayed aa multipletmultiplet signalsignal centeringcentering atat δδ == 4.61 correspondingcorresponding toto thethe SiHSiH22 protons, which is shifted upfieldupfield byby 0.890.89 ppmppm inin comparisoncomparison withwith thatthat ofof4 4.. TheThe 3131P{1H} NMR spectrum of 3 showedshowed twotwo 2 195195 1 1 1 1 doublets ( JJP–PP–P == 21 21 Hz) Hz) with with Pt Ptsatellites satellites at δ at = δ30.5= 30.5 ( JPt–P( J=Pt–P 2247= 2247Hz) and Hz) 34.5and (34.5JPt–P (= J1837Pt–P =Hz), 1837 which Hz), 1 1 1 1 whichare close are to close those to thoseof 2 [ ofδ =2 33.8[δ = 33.8( JPt–P ( =JPt–P 2183= Hz) 2183 and Hz) 34.5 and 34.5( JPt–P( =JPt–P 1963= Hz)]. 1963 Hz)]The .observation The observation of P–P of P–Pcoupling coupling indicates indicates a large a deviation large deviation of the P–Pt–P of the P–Pt–Pangle from angle 90° from of the 90 ideal◦ of thesquare ideal planar square geometry planar geometryaround the around Pt(II) center the Pt(II) (vide center infra). (videIn contrast, infra). the In 31 contrast,P{1H} resonances the 31P{ 1forH} 4 resonances were observed for 4aswere two 1 1 1 1 observedsinglets at asδ = two 69.2 singlets( JPt–P = 1809 at δ Hz)= 69.2 and (85.3JPt–P ( JPt–P= 1809 = 1678 Hz) Hz), and respectively, 85.3 ( JPt–P which= 1678 are Hz), relatively respectively, shifted 1 1 whichdownfield are relative relatively to shiftedthose of downfield 2 and 3. The relative larger to J thosePt–P values of 2 (2183and 3Hz. Thefor 3 larger, 1809 HzJPt–P forvalues 4) are assigned to the phosphorus atom trans to the hydrido ligand, as in the case of 2. Furthermore, the 29Si{1H} NMR spectra of 3 and 4 showed a doublet of doublets signals at δ = −39.0 (2JSi–P = 167, 12 Hz) for 3, and −44.6 (2JSi–P = 173, 11 Hz) for 4, which were accompanied by 195Pt satellites of 1207 Hz for 3 and 1253 Hz for 4, respectively.

Inorganics 2017, 5, 72 4 of 11

(2183 Hz for 3, 1809 Hz for 4) are assigned to the phosphorus atom trans to the hydrido ligand, as in the case of 2. Furthermore, the 29Si{1H} NMR spectra of 3 and 4 showed a doublet of doublets signals 2 2 at δ = −39.0 ( JSi–P = 167, 12 Hz) for 3, and −44.6 ( JSi–P = 173, 11 Hz) for 4, which were accompanied 195 Inorganicsby InorganicsPt 2017 satellites, 20175, 72, 5 ,of 72 1207 Hz for 3 and 1253 Hz for 4, respectively. 4 of 114 of 11

L H Ph Ph Cy Cy DPPF or DCPE L H Ph Ph Cy Cy DPPF or DCPE Pt P 2 Pt P P 2 L Si DPPF =Fe P DCPE = toluene, RT L Si DPPF = DCPE = toluene, RT Fe P P H H P P H H Ph Ph Cy Cy 3 (dppf, 87%) Ph Ph Cy Cy 3 4(dppf, (dcpe, 87%) 80%) 4 (dcpe, 80%) Scheme 2. Ligand-exchange reaction of [cis-PtH(SiH2Trip)(PPh3)2] 2 with chelating bis(phosphine)s. Scheme 2. cis 2 Scheme 2. Ligand-exchange reaction of [cis-PtH(SiH-PtH(SiH22Trip)(PPh3))22]] 2 withwith chelating chelating bis(phosphine)s. bis(phosphine)s. The molecular structure of DPPF-derivative 3 in the crystalline state was confirmed by X-ray The molecular structure of DPPF-derivative 3 in the crystalline state was confirmed by X-ray Thecrystallography molecular (Figurestructure 2). Theof DPPF-derivative platinum atom lies 3 in in a distortedthe crystalline square-planar state was geometry; confirmed the sum by of X-ray crystallographythe bond angles (Figure around2). The the platinum platinum atomatom liesis 360. in48°. a distorted The P1–Pt1–P2 square-planar angle is geometry;102.29(9)°, theand sum other of the crystallography (Figure 2). The platinum atom lies in a distorted square-planar geometry; the sum of bondangles angles around around the the platinum platinum atom atom are less is 360.48 than 90°,◦. The except P1–Pt1–P2 the P1–Pt1–Si1 angle isangl 102.29(9)e [95.19(9)°].◦, and The other Pt–Si angles the bond angles around the platinum atom is 360.48°. The P1–Pt1–P2 angle is 102.29(9)°, and other around[2.331(3) the platinum Å] and atom two arePt–P less bond than lengths 90◦, except [2.286(2), the P1–Pt1–Si1 2.319(2) Å] angle are [95.19(9)comparable◦]. Theto those Pt–Si [2.331(3)of the Å] angles around the platinum atom are less than 90°, except the P1–Pt1–Si1 angle [95.19(9)°]. The Pt–Si and twocorresponding Pt–P bond lengthsDPPF-ligated [2.286(2), hydrido 2.319(2) complex Å] are comparable [PtH(SiHPh to2 those)(dppf)] of the[2.3366(4), corresponding 2.2830(4), DPPF-ligated and [2.331(3)2.3192(4) Å] andÅ, respectively] two Pt–P [40].bond lengths [2.286(2), 2.319(2) Å] are comparable to those of the hydrido complex [PtH(SiHPh2)(dppf)] [2.3366(4), 2.2830(4), and 2.3192(4) Å, respectively] [40]. corresponding DPPF-ligated hydrido complex [PtH(SiHPh2)(dppf)] [2.3366(4), 2.2830(4), and 2.3192(4) Å, respectively] [40].

FigureFigure 2. ORTEP 2. ORTEP of of [PtH(SiH [PtH(SiH22Trip)(dppf)]Trip)(dppf)] 3 350%50% thermal thermal ellipsoids, ellipsoids, a solvation a solvation CH2Cl2 CHmolecule,2Cl2 molecule, and and hydrogenhydrogen atoms, atoms, except except H1, H1,H2, and H2, H3 and were H3 omitted were omittedfor clarity. for Selected clarity. bond Selected lengths bond(Å) and lengths bond (Å) and bondangles angles(°): Pt1–Si1 (◦): = Pt1–Si1 2.331(3), = Pt1–P1 2.331(3), = 2.286(2) Pt1–P1, Pt1–P2 = 2.286(2), = 2.319(2),Pt1–P2 Pt1–H1 = 2.319(2) = 1.687(10),, Pt1–H1 Si1–C1 = 1.687(10) = ,

Si1–C11.920(10), = 1.920(10) P1–Pt1–P2, P1–Pt1–P2 = 102.29(9), = 102.29(9), Si1–Pt1–P1 Si1–Pt1–P1 = 95.19( =9), 95.19(9), Si1–Pt1–H1Si1–Pt1–H1 = 76(5), P2–Pt1–H1 = 76(5), P2–Pt1–H1 = 87(5), Si1– = 87(5), Si1–Pt1–P2Pt1–P2 == 162.10(9), P1–Pt1–H1 P1–Pt1–H1 = 171(5). = 171(5). Figure 2. ORTEP of [PtH(SiH2Trip)(dppf)] 3 50% thermal ellipsoids, a solvation CH2Cl2 molecule, and

hydrogenIt is well atoms, known except that H1, H2, and H3 were omitted (PMe3) isfor a strongclarity. σ Selected-donating bond ligand lengths for a (Å) wide and variety bond It is well known that trimethylphosphine (PMe3) is a strong σ-donating ligand for a wide angles (°): Pt1–Si1 = 2.331(3), Pt1–P1 = 2.286(2), Pt1–P2 = 2.319(2), Pt1–H1 = 1.687(10), Si1–C1 = varietyof oftransition-metal transition-metal complexes. complexes. Therefore, Therefore, one can one canreasonably reasonably expect expect the formation the formation of of 1.920(10),[PtH(SiH 2P1–Pt1–P2Trip)(PMe 3)=2 ]102.29(9), in a similar Si1–Pt1–P1 ligand-exchange = 95.19( reaction9), Si1–Pt1–H1 of 2 with = PMe76(5),3. However,P2–Pt1–H1 we = found87(5), Si1–that [PtH(SiH2Trip)(PMe3)2] in a similar ligand-exchange reaction of 2 with PMe3. However, we found Pt1–P2the reaction = 162.10(9), of 2 withP1–Pt1–H1 2.2 equivalents = 171(5). of PMe3 in toluene at room temperature did not proceed that the reaction of 2 with 2.2 equivalents of PMe in toluene at room temperature did not proceed completely, which resulted in the formation of 3[PtH(SiH2Trip)(PMe3)(PPh3)] (5), where the PPh3 completely, which resulted in the formation of [PtH(SiH2Trip)(PMe3)(PPh3)] (5), where the PPh3 ligand Itligand is well trans known to hydrido that trimethylphosphine in 2 is exchanged with (PMe a PMe3) 3is ligand a strong (Scheme σ-donating 3). Complex ligand 5 was for isolateda wide varietyas trans to hydrido in 2 is exchanged with a PMe ligand (Scheme1 3). Complex 5 was isolated as colorless of transition-metalcolorless crystals incomplexes. quantitative Therefore,yield after3 workup.one can In thereasonably H NMR spectrum expect of the5 at 298formation K, the of characteristic broad doublet signal due to the platinum hydride was observed centering at δ = −1.91 [PtH(SiH2Trip)(PMe3)2] in a similar ligand-exchange reaction of 2 with PMe3. However, we found that the reaction of 2 with 2.2 equivalents of PMe3 in toluene at room temperature did not proceed completely, which resulted in the formation of [PtH(SiH2Trip)(PMe3)(PPh3)] (5), where the PPh3 ligand trans to hydrido in 2 is exchanged with a PMe3 ligand (Scheme 3). Complex 5 was isolated as colorless crystals in quantitative yield after workup. In the 1H NMR spectrum of 5 at 298 K, the characteristic broad doublet signal due to the platinum hydride was observed centering at δ = −1.91

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Inorganicscrystals 2017 in quantitative, 5, 72 yield after workup. In the 1H NMR spectrum of 5 at 298 K, the characteristic5 of 11 broad doublet signal due to the platinum hydride was observed centering at δ = −1.91 with splitting by 31 1 2 31 1 2 195 1 1 195 1 1 withP– splittingH( JP(trans by)–H P–= 157H ( Hz)JP(trans and)–H = 157Pt– Hz)H( andJPt–H =Pt– 899H Hz) ( JPt–H couplings. = 899 Hz) The couplings. SiH2 protons The alsoSiH2 appeared protons alsoas a appeared broadInorganics multiplet 2017 as, 5a, 72broad at δ multiplet= 5.95, which at δ = is 5.95, shifted which downfield is shifted relative downfield to those relative ofthe to those above of complexes the5 of 11 above complexes2–4 (δ = 4.68–5.50) 2–4 (δ =. 4.68–5.50). The 31P{1H} The NMR 31P{ spectrum1H} NMR of spectrum5 at 298 K of exhibited 5 at 298 twoK exhibited nonequivalent two nonequivalent broad singlet 31 1 2 195 1 1 broadsignalswith singlet at splittingδ = −signals22.9 by and atP– δ 37.4,H = ( −J22.9P( withtrans)–H and two= 157 37.4, sets Hz) with ofand195 twoPtPt– satellites setsH ( JofPt–H 195 of= Pt899 2115 satellites Hz) and couplings. 1833 of 2115 Hz. The and The SiH 1833 former2 protons Hz. signal The also appeared as a broad multiplet at δ = 5.95, which is shifted downfield1 relative to those31 1 of the above 31 formerwas assigned signal towas the assigned PMe3 trans to theto the PMe hydrido3 trans ligandto the usinghydrido a non ligandH-decoupled using a non PH-decoupled NMR technique P complexes 2–4 (δ = 4.68–5.50). The 31P{1H} NMR spectrum of 5 at 298 K exhibited two nonequivalent NMRat 253 technique K. The 29Si{ at 1253H} NMRK. The spectrum 29Si{1H} NMR of 5 at spectrum 223 K featured of 5 at 223 one K29 Sifeatured resonance one as29Si a resonance broad doublet as a broad singlet signals at δ = −22.9 and 37.4, with two sets of 195Pt satellites of 2115 and 1833 Hz. The broadsignal doublet at δ = − signal43.9 (2 atJ δ == −43.9 151 Hz).(2JSi–P The= 151 broadening Hz). The broadening of NMR signals of NMR possibly signals implies possibly the implies existence the former signal was Si–Passigned to the PMe3 trans to the hydrido ligand using a non 1H-decoupled 31P existenceof theNMR Si–H of technique σthe-complex Si–H at 253σ intermediate-complex K. The 29 Si{intermediate1H}6 in NMR the NMRspectrum 6 in time the of NMR scale5 at 223 [38time K, 41featured ,scale42]. Unfortunately, [38,41,42].one 29Si resonance Unfortunately, attempts as a to attemptsprobebroad further to doublet probe the signalfurther fluxional at theδ = behavior −fluxional43.9 (2JSi–P of =behavior 1515 by Hz). VT Theof (variable 5 broadening by VT temperature)-NMR(variable of NMR temperature)-NMR signals possibly in solution implies in revealedsolution the revealedno appreciableexistence no appreciable ofchanges the Si–H in changesσ-complex spectroscopic in intermediate spectroscopic features 6 in by features the1H NMR and by31 time P1H NMR scaleand .31[38,41,42].P NMR spectroscopy.Unfortunately, The molecular The molecularstructureattempts ofstructure5 tois probe also of determinedfurther 5 is also the determined fluxional by X-ray behavior by analysis, X-ray of 5 analysis, asby shownVT (variable as in shown Figure temperature)-NMR in3 .Figure Distortions 3. Distortions infrom solution square from squareplanarrevealed geometryplanar nogeometry appreciable at the platinum at the changes platinum center in spectroscopic werecenter observed, were features observed, similar by similar to1H theand cases 31toP theNMR of cases2 andspectroscopy. of4 .2 Theand Pt–Si 4 .The The bond Pt– Silength bondmolecular of length5 [2.3414(13) structure of 5 [2.3414(13) Å]of 5 is is almost also Å] determined is equal almost to by thoseequal X-ray ofto analysis, 2those[2.3458(9) of as 2 shown [2.3458(9) Å] and in Figure4 Å][2.331(3) and3. Distortions 4 Å].[2.331(3) As from expected, Å]. As square planar geometry at the platinum center were observed, similar to the cases of 2 and 4. The Pt– expected,the Pt1–P1 the bond Pt1–P1 length bond for length the PMe for ligandthe PMe of35 ligand[2.2978(12) of 5 [2.2978(12) Å] is shortened Å] is shortened compared compared with the Pt1–P2 with Si bond length of 5 [2.3414(13) Å]3 is almost equal to those of 2 [2.3458(9) Å] and 4 [2.331(3) Å]. As thebond Pt1–P2 length bond forthe length PPh 3forligand the PPh of 53 ligand[2.3203(11) of 5 [2.3203(11) Å] due to the Å] different due to the ligands different in the ligandstrans positionsin the trans of expected, the Pt1–P1 bond length for the PMe3 ligand of 5 [2.2978(12) Å] is shortened compared with positionsthe phosphorus of the atoms. phosphorus While onlyatoms. a few While cationic only platinum a few cationic complexes platinum containing complexes different containing phosphine the Pt1–P2 bond length for the PPh3 ligand of 5 [2.3203(11) Å] due to the different ligands in the trans differentligandspositions have phosphine beenof the reported ligandsphosphorus have [43 –atoms.45 been], complex reportedWhile only5 is[43–45], thea few first complexcationic example platinum 5 is of the a neutral firstcomplexes example platinum containing of a complex neutral platinumbearingdifferent a complex weakly phosphine electron-donating bearing ligands a weakly have been PPhelectron-donating3 reportedand strongly [43–45], electron-donatingPPh complex3 and strongly5 is the first PMeelectron-donating example3. of a neutral PMe 3. platinum complex bearing a weakly electron-donating PPh3 and strongly electron-donating PMe3. Ph3P H PMe3 Ph3P Pt H 2 PMe3 Me P Pt Si 2 toluene, RT 3 Me3P Si toluene, RT H H H H 5 (94%) 5 (94%) Scheme 3. Ligand-exchange reaction of [cis-PtH(SiH2Trip)(PPh3)2] 2 with trimethylphosphine (PMe3). SchemeScheme 3. Ligand-exchange 3. Ligand-exchange reaction reaction of of [cis [cis-PtH(SiH-PtH(SiH22Trip)(PPh3)32)]2 2] with2 with trimethylphosphine trimethylphosphine (PMe (PMe3). 3).

Figure 3. ORTEP of [PtH(SiH2Trip)(PMe3)(PPh3)] 5 50% thermal ellipsoids, a solvation CH2Cl2 Figure 3. ORTEP of [PtH(SiH2Trip)(PMe3)(PPh3)] 5 50% thermal ellipsoids, a solvation CH2Cl2 molecule,molecule, and and hydrogen hydrogen atoms, atoms, except except H1, H1, H2, H2, andand H3 were were omitted omitted for for clarity. clarity. Selected Selected bond bond lengths lengths Figure 3. ORTEP of [PtH(SiH2Trip)(PMe3)(PPh3)] 5 50% thermal ellipsoids, a solvation CH2Cl2 (Å) and(Å) bondand bond angles angles (◦): (°): Pt1–Si1 Pt1–Si1 = = 2.3414(13), 2.3414(13), Pt1–P1Pt1–P1 = = 2.2978(12), 2.2978(12), Pt1–P2 Pt1–P2 = 2.3203(11), = 2.3203(11), Pt1–H1 Pt1–H1 = 1.44(6), = 1.44(6), molecule,Si1–C1 and = 1.930(5), hydrogen P1–Pt1–P2 atoms, = except 103.47(4), H1, Si1–Pt1–P1 H2, and H3 = 92.34(4), were omitted Si1–Pt1–H1 for clarity. = 75(2), SelectedP2–Pt1–H1 bond = 89(2), lengths Si1–C1 = 1.930(5), P1–Pt1–P2 = 103.47(4), Si1–Pt1–P1 = 92.34(4), Si1–Pt1–H1 = 75(2), P2–Pt1–H1 = 89(2), (Å) andSi1–Pt1–P2 bond angles = 164.19(4), (°): Pt1–Si1 P1–Pt1–H1 = 2.3414(13), = 167(2). Pt1–P1 = 2.2978(12), Pt1–P2 = 2.3203(11), Pt1–H1 = 1.44(6), Si1–Pt1–P2 = 164.19(4), P1–Pt1–H1 = 167(2). Si1–C1 = 1.930(5), P1–Pt1–P2 = 103.47(4), Si1–Pt1–P1 = 92.34(4), Si1–Pt1–H1 = 75(2), P2–Pt1–H1 = 89(2), A plausible formation mechanism for 5 is shown in Scheme 4. According to the stronger trans Si1–Pt1–P2 = 164.19(4), P1–Pt1–H1 = 167(2). influence of the silyl ligand than that of the hydrido ligand, the ligand-exchange of a PPh3 trans to

A plausible formation mechanism for 5 is shown in Scheme 4. According to the stronger trans influence of the silyl ligand than that of the hydrido ligand, the ligand-exchange of a PPh3 trans to

Inorganics 2017, 5, 72 6 of 11

InorganicsA plausible 2017, 5, 72 formation mechanism for 5 is shown in Scheme4. According to the stronger trans6 of 11 influence of the silyl ligand than that of the hydrido ligand, the ligand-exchange of a PPh3 trans to silyl ligandsilyl ligand takes placetakes toplace yield to the yield intermediate the intermediate50 in the 5 first′ in the step, first while step,5 mightwhile be5 might formed be directly formed from directly the correspondingfrom the corresponding coordinatively coordinatively unsaturated intermediate unsaturated(3-coordinated intermediate 14-electron (3-coordinated complexes) 14-electron[46,47]. Then,complexes) the intramolecular [46,47]. Then, interchangethe intramolecular of coordination interchange environments of coordination between environments the silyl and between hydrido the ligandssilyl and through hydrido theligands Si–H throughσ-complex the Si–H intermediate σ-complex6 intermediatewould occur, 6 would probably occur, due probably to the due steric to 0 repulsionthe steric repulsion between thebetween bulky the 9-triptycyl bulky 9-triptycyl group on group the silicon on the atomsilicon and atom the andcis -PPhthe cis3 ligand-PPh3 ligand in 5 . Finally,in 5′. Finally, the corresponding the corresponding complex complex5 was 5 was obtained obtained as theas the thermodynamic thermodynamic product. product. As As anotheranother pathway,pathway, it it is is likely likely that that the the direct direct formation formation of of5 5is is caused caused by by an an initial initial dissociation dissociation of of the the PPh PPh33 ligandligand atat thethe transtransposition position ofof thethe hydridohydrido ligandligandin in2 2due dueto tosteric stericreason. reason.

Scheme 4. Plausible reaction pathway for the formation of [PtH(SiH2Trip)(PMe3)(PPh3)] 5. Scheme 4. Plausible reaction pathway for the formation of [PtH(SiH2Trip)(PMe3)(PPh3)] 5.

3.3. MaterialsMaterials andand MethodsMethods

3.1. General Procedures 3.1. General Procedures All of the experiments were performed under an atmosphere unless otherwise noted. All of the experiments were performed under an argon atmosphere unless otherwise noted. were dried by standard methods and freshly distilled prior to use. 1H, 13C, and 31P Solvents were dried by standard methods and freshly distilled prior to use. 1H, 13C, and 31P NMR NMR spectra were recorded on Bruker DPX-400 or DRX-400 (400, 101 and 162 MHz, respectively), spectra were recorded on Bruker DPX-400 or DRX-400 (400, 101 and 162 MHz, respectively), Avance- Avance-500 (500, 126 and 202 MHz, respectively) (Karlsruhe, Germany) spectrometers using CDCl3 500 (500, 126 and 202 MHz, respectively) (Karlsruhe, Germany) spectrometers using CDCl3 or C6D6 or C D as the at room temperature. 29Si NMR spectra were recorded on Bruker Avance-500 as the6 6 solvent at room temperature. 29Si NMR spectra were recorded on Bruker Avance-500 (Karlsruhe, Germany) or JEOL EX-400 (Tokyo, Japan) (99.4 and 79.3 MHz, respectively) spectrometers (Karlsruhe, Germany) or JEOL EX-400 (Tokyo, Japan) (99.4 and 79.3 MHz, respectively) using CDCl3, CD2Cl2,C6D6, or THF-d8 as the solvent at room temperature, unless otherwise noted. spectrometers using CDCl3, CD2Cl2, C6D6, or THF-d8 as the solvent at room temperature, unless IR spectra were obtained on a Perkin-Elmer System 2000 FT-IR spectrometer (Walham, MA, USA). otherwise noted. IR spectra were obtained on a Perkin-Elmer System 2000 FT-IR spectrometer Elemental analyses were carried out at the Molecular Analysis and Science Center of Saitama (Walham, MA, USA). Elemental analyses were carried out at the Molecular Analysis and Life Science University. All of the melting points were determined on a Mel-Temp capillary tube apparatus Center of Saitama University. All of the melting points were determined on a Mel-Temp capillary 2 (Stafford, UK) and are uncorrected. 9-Triptycylsilane (TripSiH3, 1)[48] and [Pt(η -C2H4)(PPh3)2][49] tube apparatus (Stafford, UK) and are uncorrected. 9-Triptycylsilane (TripSiH3, 1) [48] and [Pt(η2- were prepared according to the reported procedures. C2H4)(PPh3)2] [49] were prepared according to the reported procedures.

3.1.1. [cis-PtH(SiH2Trip)(PPh3)2](2) 3.1.1. [cis-PtH(SiH2Trip)(PPh3)2] (2) 2 A solution of TripSiH3 1 (50.9 mg, 0.179 mmol) and [Pt(η -C2H4)(PPh3)2] (149.3 mg, 0.199 mmol) A solution of TripSiH3 1 (50.9 mg, 0.179 mmol) and [Pt(η2-C2H4)(PPh3)2] (149.3 mg, 0.199 mmol) in toluene (3 mL) was stirred at room temperature for 1 h to form a pale yellow solution. After the in toluene (3 mL) was stirred at room temperature for 1 h to form a pale yellow solution. After the removal of the solvent in vacuo, the residual colorless solid was purified by washing with hexane to removal of the solvent in vacuo, the residual colorless solid was purified by washing with hexane to give [cis-PtH(SiH2Trip)(PPh3)2](2) (164.3 mg, 91%) as colorless crystals. give [cis-PtH(SiH2Trip)(PPh3)2] (2) (164.3 mg, 91%) as colorless crystals. 1 2 2 1 H NMR (400 MHz, CDCl3): δ = −2.15 (dd, JH–P(trans) = 157, JH–P(cis) = 19, JH–Pt = 958 Hz, 1H NMR (400 MHz, CDCl3): δ = −2.15 (dd, 2JH–P(trans) = 157, 2JH–P(cis) = 19, 1JH–Pt = 958 Hz, 1H, PtH), 4.68 1H, PtH), 4.68 (m, 2H, SiH2), 5.28 (s, 1H, TripCH), 6.83–6.89 (m, 6H, Ar), 7.02–7.06 (m, 6H, Ar), (m, 2H, SiH2), 5.28 (s, 1H, TripCH), 6.83–6.89 (m, 6H, Ar), 7.02–7.06 (m, 6H, Ar), 7.15–7.31 (m, 21H, 7.15–7.31 (m, 21H, Ar), 7.49 (t, J = 7 Hz, 6H, Ar), 7.81 (d, J = 7 Hz, 3H, Ar). 13C{1H} NMR Ar), 7.49 (t, J = 7 Hz, 6H, Ar), 7.81 (d, J = 7 Hz, 3H, Ar). 13C{1H} NMR (101 MHz, CDCl3): δ = 46.6 (101 MHz, CDCl ): δ = 46.6 (TripC), 55.3 (TripCH), 122.7 (Ar(CH)), 123.7 (Ar(CH) × 2), 126.2 (Ar(CH)), (TripC), 55.3 (TripCH),3 122.7 (Ar(CH)), 123.7 (Ar(CH) × 2), 126.2 (Ar(CH)), 127.8 (Ar(CH)), 127.9 127.8 (Ar(CH)), 127.9 (Ar(CH)), 129.4 (Ar(CH)), 129.6 (Ar(CH)), 134.1 (Ar(CH)), 134.2 (Ar(CH)), (Ar(CH)), 129.4 (Ar(CH)), 129.6 (Ar(CH)), 134.1 (Ar(CH)), 134.2 (Ar(CH)), 133.7–134.8 (m, Ar(C)), 135.5 (d, 1JC–P = 38 Hz, Ar(C)), 148.4 (Ar(C)), 149.5 (Ar(C)). 31P{1H} NMR (162.0 MHz, CDCl3): δ = 33.8 (d, 2JP–P = 15, 1JP–Pt = 2183 Hz), 34.5 (d, 2JP–P = 15, 1JP–Pt = 1963 Hz). 29Si{1H} NMR (79.3 MHz, CD2Cl2): δ =

Inorganics 2017, 5, 72 7 of 11

1 31 1 133.7–134.8 (m, Ar(C)), 135.5 (d, JC–P = 38 Hz, Ar(C)), 148.4 (Ar(C)), 149.5 (Ar(C)). P{ H} NMR 2 1 2 1 (162.0 MHz, CDCl3): δ = 33.8 (d, JP–P = 15, JP–Pt = 2183 Hz), 34.5 (d, JP–P = 15, JP–Pt = 1963 Hz). 29 1 2 2 1 Si{ H} NMR (79.3 MHz, CD2Cl2): δ = −40.6 (dd, JSi–P(trans) = 161, JSi–P(cis) = 15, JSi–Pt = 1220 Hz). −1 IR (KBr, cm ): ν = 2041 (Pt–H), 2080 (Si–H). Anal. Calcd. for C56H46P2PtSi: C, 66.99; H, 4.62. Found: C, 66.55; H, 4.61. Melting point: 123 ◦C (dec.).

3.1.2. [PtH(SiH2Trip)(dppf)] (3) A solution of 2 (40.5 mg, 0.040 mmol) and DPPF (28.2 mg, 0.048 mmol) in toluene (3 mL) was stirred at room temperature for 5 h. After the removal of the solvent in vacuo, the residual colorless solid was purified by washing with Et2O and hexane to give [PtH(SiH2Trip)(dppf)] (3) (37.1 mg, 0.035 mmol, 87%) as yellow crystals.

1 2 2 1 H NMR (400 MHz, CDCl3): δ = −1.62 (dd, JH–P(trans) = 164, JH–P(cis) = 20, JH–Pt = 995 Hz, 1H, PtH), 3.86 (s, 2H, Cp), 4.20 (s, 2H, Cp), 4.37 (s, 2H, Cp), 4.58–4.64 (m, 4H, Cp and SiH2), 5.30 (s, 1H, TripCH), 6.87–6.89 (m, 6H, Ar), 7.26 (m, 6H, Ar), 7.41 (br, 6 H, Ar), 7.66–7.81 (m, 14H, Ar). 13C{1H} NMR 3 3 (101 Hz, CDCl3): δ = 46.5 (m, TripC), 55.2 (TripCH), 71.3 (d, JC–P = 5 Hz, Cp(CH)), 72.1 (d, JC–P = 6 Hz, 2 2 1 Cp(CH)), 74.5 (d, JC–P = 7 Hz, Cp(CH)), 75.6 (d, JC–P = 8 Hz, Cp(CH)), 79.3 (dd, JC–P = 42, 3 1 3 JC–P = 5 Hz, Cp(C)), 80.7 (dd, JC–P = 47, JC–P = 6 Hz, Cp(C)), 122.7 (Ar(CH)), 123.71 (Ar(CH)), 3 3 123.68 (Ar(CH)), 126.4 (Ar(CH)), 127.7 (d, JC–P = 11 Hz, Ar(CH)), 128.0 (d, JC–P = 10 Hz, Ar(CH)), 2 2 129.9 (Ar(CH)), 130.1 (Ar(CH)), 134.3 (d, JC–P = 13 Hz, Ar(CH)), 134.6 (d, JC–P = 14 Hz, Ar(CH)), 1 31 1 134.8–135.5 (m, Ar(C)), 136.2 (d, JC–P = 43 Hz, Ar(C)), 148.4 (Ar(C)), 149.7 (Ar(C)). P{ H} NMR 2 1 2 1 (202 MHz, CDCl3): δ = 30.5 (d, JP–P = 21 Hz, JPt–P = 2247 Hz), 34.5 (d, JP–P = 21, JPt–P = 1837 Hz). 29 1 2 2 1 Si{ H} NMR (79.3 MHz, CDCl3): δ = −39.0 (dd, JSi–P(trans) = 167, JSi–P(cis) = 12, JSi–Pt = 1207 Hz). −1 IR (KBr, cm ): ν = 2055 (Pt–H), 2081 (Si–H). Anal. Calcd. for C54H44FeP2PtSi: C, 62.73; H, 4.29. Found: C, 62.70; H, 4.27. Melting point: 183 ◦C (dec.).

3.1.3. [PtH(SiH2Trip)(dcpe)] (4) A solution of 2 (35.6 mg, 0.035 mmol) and DCPE (18.8 mg, 0.044 mmol) in toluene (3 mL) was stirred at room temperature for 5 h. After the removal of the solvent in vacuo, the residual colorless solid was purified by washing with Et2O and hexane to give [PtH(SiH2Trip)(dcpe)] (4) (25.5 mg, 0.028 mmol, 80%) as colorless crystals.

1 2 2 1 H NMR (500 MHz, CDCl3): δ = −0.45 (dd, JH–P(trans) = 165, JH–P(cis) = 13, JPt–H = 1004 Hz, 1H, PtH), 1.16–1.51 (m, 20H, Cy), 1.65–1.86 (m, 24H, Cy), 2.16–2.19 (m, 2H, Cy), 2.30–2.37 (m, 2H, Cy), 2 3 2 5.32 (s, 1H, TripCH), 5.50 (dd, JH–H = 15, JH–P(trans) = 6, JPt–H = 31 Hz, 2H, SiH2), 6.84–6.90 (m, 6H, Ar), 13 1 7.30–7.32 (d, J = 7 Hz, 3H, Ar), 7.94–7.96 (d, J = 7 Hz, 3H, Ar). C{ H} NMR (101 Hz, CDCl3): 3 3 3 δ = 23.2 (dd, JC–P = 21, 16 Hz, PCH2), 26.2 (dd, JC–P = 23, 21 Hz, PCH2), 26.9 (d, JC–P = 14 Hz, 3 3 3 PCy(CH2)), 26.4 (d, JC–P = 13 Hz, PCy(CH2)), 26.8 (d, JC–P = 10 Hz, PCy(CH2)), 27.0 (d, JC–P = 12 Hz, PCy(CH2)), 28.9 (m, PCy(CH2) × 2), 29.7 (m, PCy(CH2)), 35.3–35.8 (m, PCy(CH) × 2), 46.8 (TripC), 55.4 (TripCH), 122.7 (Ar(CH)), 123.6 (Ar(CH)), 126.9 (Ar(CH)), 148.6 (Ar(C)), 159.2 (Ar(C)). 31P{1H} 1 1 29 1 NMR (162 Hz, CDCl3): δ = 69.2 (s, JPt–P = 1809 Hz), 85.3 (s, JPt–P = 1678 Hz). Si{ H} NMR 2 2 1 −1 (79.3 MHz, CD2Cl2): δ = −44.6 (dd, JSi–P(trans) = 173, JSi–P(cis) = 11, JSi–Pt = 1253 Hz). IR (KBr, cm ): ν = 2057 (Pt–H), 2081 (Si–H). Anal. Calcd for C46H64P2PtSi: C, 61.24; H, 7.15. Found: C, 61.10; H, 7.10. Melting point: 134 ◦C (dec.).

3.1.4. [PtH(SiH2Trip)(PMe3)(PPh3)] (5)

A toluene solution of PMe3 (1.0 M, 0.2 mL, 0.200 mmol) was added to a solution of 2 (98.0 mg, 0.098 mmol) in toluene (3.5 mL) at room temperature. The reaction mixture was stirred at room temperature for 30 min. After the removal of the solvent in vacuo, the residual colorless solid was purified by washing with Et2O and hexane to give [PtH(SiH2Trip)(PMe3)(PPh3)] 5 (75.6 mg, 94%) as colorless crystals. Inorganics 2017, 5, 72 8 of 11

1 2 1 H NMR (400 MHz, C6D6): δ = −1.91 (d, JH–P(trans) = 157, JH–Pt = 899 Hz, 1H, PtH), 1.03–1.11 (m, 9H, PMe), 5.34 (s, 1H, TripCH), 5.95–5.97 (m, 2H, SiH2), 6.82–6.97 (m, 15H, Ar), 13 1 7.31 (d, J = 7 Hz, 3H, Ar), 7.57 (br, 6H, Ar), 8.50 (d, J = 7 Hz, 3H, Ar). C{ H}-NMR (101 Hz, CDCl3): δ = 16.4–17.1 (m, PMe), 53.6 (TripC), 55.4 (TripCH), 123.0 (Ar(CH)), 123.9 (Ar(CH)), 124.1 (Ar(CH)), 3 2 126.5 (Ar(CH)), 128.5 (d, JC–P = 10 Hz, Ar(CH)), 130.0 (Ar(CH)), 134.4 (d, JC–P = 13 Hz, Ar(CH)), 1 31 1 135.6 (d, JC–P = 36 Hz, Ar(CH), 148.5 (Ar(C)), 149.7 (Ar(C)). P{ H}-NMR (162 Hz, C6D6): 1 1 29 1 δ = −22.9 (s, JPt–P = 2115 Hz), 37.4 (br, JPt–P = 1833 Hz). Si{ H}-NMR (79.3 MHz, THF-d8, 223 K) 2 −1 δ −43.9 (d, JSi–P(trans) = 151 Hz). IR (KBr, cm ) ν = 2029 (Pt–H), 2054 (Si–H). Anal. Calcd for ◦ C41H40P2PtSi: C, 60.21; H, 4.93. Found: C, 60.57; H, 5.00. Melting point: 115 C (dec.).

3.2. X-ray Crystallographic Studies of 2, 3, and 5 Colorless single crystals of 2 were grown by the slow evaporation of its saturated toluene solution, and single crystals of 3 and 5 were grown by the slow evaporation of its saturated CH2Cl2 and hexane solution. The intensity data were collected at 103 K on a Bruker AXS SMART diffractometer (Karlsruhe, Germany) employing graphite-monochromatized Mo Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods and refined by full-matrix least-squares procedures on F2 for all reflections (SHELX-97) [50]. Hydrogen atoms, except for the PtH and SiH of 2, 3, and 5, were located by assuming ideal geometry, and were included in the structure calculations without further refinement of the parameters. Full details of the crystallographic analysis and accompanying cif files (see Supplementary Materials) may be obtained free of charge from the Cambridge Crystallographic Data Centre (CCDC numbers 1577277, 1577278, and 1577279) via http://www.ccdc.cam.ac.uk/conts/retrieving.html (or from the CCDC, 12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44-1223-336033; E-mail: [email protected]).

3.2.1. [cis-PtH(SiH2Trip)(PPh3)2](2)

C56H46P2PtSi, C7H8, MW = 1096.18, triclinic, space group P-1, a = 12.7971(6) Å, b = 13.4847(6) Å, c = 14.8861(7) Å, α = 99.2791(10)◦, β = 99.2791(10)◦, γ = 90.3020(10)◦, V = 2472.4(2) Å3, Z = 2, −3 Dcalc. = 1.472 g·cm , R1 (I > 2σI) = 0.0310, wR2 (all data) = 0.0718 for 11639 reflections and 617 parameters, GOF = 1.025.

3.2.2. [PtH(SiH2Trip)(dppf)] (3)

C54H44FeP2PtSi, CH2Cl2, MW = 1118.79, monoclinic, space group P21, a = 12.2585(6) Å, ◦ 3 −3 b = 15.5003(7) Å, c = 12.9367(6) Å, β = 110.8060(10) , V = 2297.81(19) Å , Z = 2, Dcalc = 1.617 g·cm , R1 (I > 2σI) = 0.0484, wR2 (all data) = 0.1171 for 8350 reflections, 571 parameters, and 2 restraints, GOF = 1.018.

3.2.3. [PtH(SiH2Trip)(PMe3)(PPh3)] (5)

C41H40P2PtSi, CH2Cl2, MW = 902.78, orthorhombic, space group Pbca, a = 15.9074(6) Å, 3 −3 b = 20.9224(8) Å, c = 22.6113(9) Å, V = 7525.5(5) Å , Z = 8, Dcalc = 1.594 g·cm , R1 (I > 2σI) = 0.0325, wR2 (all data) = 0.0706 for 7011 reflections and 448 parameters, GOF = 1.026.

4. Conclusions We have demonstrated that the oxidative addition of the sterically bulky primary silane, 2 TripSiH3 1 with [Pt(η -C2H4)(PPh3)2] in toluene, resulted in the formation of the mononuclear (hydrido)(dihydrosilyl) complex [cis-PtH(SiH2Trip)(PPh3)2] 2. The ligand-exchange reactions of 2 with free chelating bis(phosphine)s such as DPPF or DCPE resulted in the formations of a series of (hydrido)(dihydrosilyl) complexes [PtH(SiH2Trip)(L)] (3: L = dppf, 4: L = dcpe). In contrast, the reaction of 2 with an excess amount of PMe3 in toluene quantitatively produced [PtH(SiH2Trip)(PMe3)(PPh3)] 5. The latter is of particular interest, as it represents the first platinum Inorganics 2017, 5, 72 9 of 11

complex having different simple phosphine ligands such as a weakly electron-donating PPh3 and a strongly electron-donating PMe3. Further investigations on the reactivity of these complexes are currently in progress.

Supplementary Materials: The following are available online at www.mdpi.com/2304-6740/5/4/72/s1, cif and cif-checked files. Acknowledgments: This work was partially supported by JSPS KAKENHI Grant Number T17K05771 (to Norio Nakata). We are grateful to Kohtaro Osakada and Makoto Tanabe (Tokyo Institute of Technology, Japan) for their assistance in measurement of 29Si NMR spectroscopy. Author Contributions: Norio Nakata, Nanami Kato, and Norio Sekizawa contributed to the synthesis and data analysis; Norio Nakata performed X-ray crystallography and wrote the manuscript; Norio Nakata and Akihiko Ishii proposed idea on the design of the experiment, reviewed and approved the final manuscript. Conflicts of Interest: The authors declare no conflicts of interest.

References

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