Metal-Catalyzed Cross-Coupling Reactions for Ferrocene Functionalization: Recent Applications in Synthesis, Material Science and Asymmetric Catalysis

Home , Kumada coupling, Negishi coupling

Mini-Reviews in Organic Chemistry, 2008, 5, 303-312 303 Metal-Catalyzed Cross-Coupling Reactions for Ferrocene Functionalization: Recent Applications in Synthesis, Material Science and Asymmetric Catalysis

V. Mamane*

Laboratoire SRSMC, Equipe Synthèse Organométallique et Réactivité, UMR CNRS-UHP 7565, Faculté des Sciences et Techniques, Nancy-Université, BP 239, 54506 Vandoeuvre-Lès-Nancy, France Abstract: Recent examples on the functionalization of the ferrocene core by means of cross-coupling reactions are reported in this review. Several methods are discussed including Negishi, Suzuki and Stille couplings for ferrocene-aryl bond formation and Sonogashira reaction for ferrocene-alkyne coupling. The properties in material science and asymmetric catalysis of the prepared ferrocenyl compounds are briefly discussed. Keywords: Cross-coupling, palladium, ferrocene, material chemistry, asymmetric catalysis.

1. INTRODUCTION decade, the Suzuki coupling has gained in interest due to the facile Due to its interesting inherent electrochemical properties and to access to the boronic species. The use of the Stille coupling is still its planar chirality, 1,2 or 1,3-disubstituted ferrocene has found a limited, particularly due to its strong sensitivity to steric hindrance. wide application in material science [1] and in homogeneous (asymmetric) catalysis [2]. Therefore, several methods to introduce sub- 2.1. Negishi Coupling stituents on the cyclopentadienyl (Cp) rings of ferrocene, have been The ferrocenylzinc intermediate necessary for the cross-coupling developed. Among these methods, metal-catalyzed cross-coupling is generated by transmetallation of the lithio derivative, which can be reactions [3] have become a powerful tool to achieve highly efficient obtained by direct lithiation of ferrocene [8], by directed orthometal- and selective transformations on one or both Cp rings. This review lation (DoM) [9] or by halogen-lithium exchange [10]. In early stud- will focus on recent examples employing cross-coupling reactions to ies, PdCl2(dppf) (dppf = diphenylphosphinoferrocene) was described create C-C and C-Heteroatom bonds directly on the ferrocene core. as the best catalyst to perform the Negishi coupling but it has been shown later that Pd(PPh3)4 and more interestingly PdCl2(PPh3)2 were 2. FERROCENE-ARYLE BOND FORMATION good catalysts for this reaction. The first example was reported in 1985 by Rosenblum’s group for the synthesis of cofacial ferrocenes A recent study on the synthesis of nonracemic C2-symmetric 1,1’- binapht-2,2’-yl bridged ferrocene (1) was reported by Kasak and [11]. Among several mono-metallated ferrocenes tested in the cross- colleagues [4]. For this purpose, they used several palladium- coupling with 1,8-diiodonaphtalene (4), the ferrocenylzinc intermedi- catalyzed reactions to couple enantiopure 2,2’-diiodo-1,1’-binaphtyl ate led to the best results with formation of the bis-coupled product (2) with 1,1’-dimetalloferrocenes (3), including the Negishi [5], Su- (5) in good yield in presence of PdCl2(dppf) as the catalyst. If one of zuki [6] and Stille [7] cross-couplings. The Negishi protocol gave the the two ferrocenes is replaced by a Cp group such as in (6), face-to- desired product with the highest yield and with stereoconservation, face metallocene triads (7) [12] and polar cofacially fixed sandwich whereas Suzuki and Stille reactions led to complete racemization of complexes (8) for Second Harmonic Generation (SHG) [13] could be binaphthyl moiety (Fig. (1)). prepared. While a “through space” interaction exists no SHG inten- sity could be observed (Fig. (2)).

Interferrocenic communication in molecules having two or more redox centers is fundamentally interesting for the study of multi- M I Pd electron transfer processes via mixed valence state derived from these + I Fe multi-metallic systems [14]. In this field, the Negishi cross-coupling has been widely used to install two or several ferrocene moities M conditions around different scaffolds. Two ferrocene fragments could be intro- (3) duced by Ogawa and colleagues on thianthrene, leading to a new type (2) 95% ee of multi-steps reversible redox organic-organometallic hybrid mole- M yield (%) ee (%) cule (9) [15]. Vollhardt’s group has succeeded in the introduction of

five ferrocene units around the Cp ring in [(C5H4)Mn(CO)3] to give ZnCl 35 95 (10) [16] and six ferrocene units around a benzene ring to furnish (11), albeit in poor yield [17]. These new multinuclear ferrocenic O Fe compounds are of potential interest since their architecture apparently B 12 0 allows for considerable electronic interaction (Fig (3)). O Another family of highly symmetric hexaferrocenyl complexes (1) SnMe3 11 0 (12) was previously described by Mamane and colleagues [18, 19]. Fig. (1). These compounds having six chiral ferrocene units around a hex- aarylbenzene core were prepared by a [2+2+2] cyclotrimerization These results explain the fact that the Negishi cross-coupling re- reaction of the corresponding alkyne monomer (13), itself obtained action has found numerous applications. However, during the last by a double Negishi coupling of chiral ferrocenylzinc (14) intermediate with bis-(p-bromophenyl)acetylene (15). Intermediate (14) was used by the same group for the design of new C3 symmetric chiral architectures (16) bearing organometallic donor-acceptor fragments *Address correspondence to this author at the Laboratoire SRSMC, Equipe Synthèse Organométallique et Réactivité, UMR CNRS-UHP 7565, Faculté des Sciences et [20]. These octupoles possessing good SHG properties showed a Techniques, Nancy-Université, BP 239, 54506 Vandoeuvre-Lès-Nancy, France; significant electronic interaction between the three 1-D arms through E-mail: [email protected] the benzene ring (Fig. (4)).

II Fe M Fe I CpZnCl

Pd (4) FcZnCl Pd FcZnCl 63-76% Fe (7) M = Fe, Co+, TiCl Pd 58% 2 + Me5 M Fe Fe Fe - PF6 (6)

(8) M = Fe, Rh, Ir (5) Fig. (2).

Fe Fe Fe Fe

Fe S Fe Mn S Fe CO (9) 71% OC CO Fe (10) 60% Fe

Fe Fe

(11) 4% Fig. (3).

O 1) Br Br CHO Fe O (15) Pd cat ZnCl OMe Fe Fe 2) Hydrolysis (13) OHC (14) 72% Co2(CO)8 85%

1) 1,3,5-Tribromobenzene, Pd 2) Hydrolysis Fe 59% CHO Fe CHO Fe Fe CHO

CHO

CHO Octupoles with high second Fe CHO order hyperpolarisabilities Fe

Fe Fe OHC OHC (16) OHC Fe (12)

Fig. (4). Metal-Catalyzed Cross-Coupling Reactions Mini-Reviews in Organic Chemistry, 2008, Vol. 5, No. 4 305

N N N N N N N N Fe Fe Fe Fe N N N Fe N R N N R = H 77% (18) 44% (19) 28% (17) R = 8-quinolyl 62% (20)(25%21) 38%

N N N N

(22)

Fe 26% (enantiomer : 18%) Fe (23) 20%

O CHO 1) N , Pd O Aldolisation- N ZnCl Br N (25) crotonisation Fe Fe Fe 2) Hydrolysis (26) (24) 60-72% Ferroceno-(iso)quinolines Fig. (5).

Several nitrogen-containing heterocycles has been used as the Negishi reactions for performing the bis-coupling of 1,1’- coupling partner of ferrocene in the Negishi cross-coupling reaction. dimetalloferrocene (3) with chiral bipiridines. The Negishi cross- Enders and colleagues described the reaction of the quinolyl group at coupling gave the best results although the yields were moderate in the 8-position with ferrocene [21]. The coupling could be realized in all cases. In their synthesis of new chiral ferroceno-(iso)quinolines good yields once or twice for furnishing compound (17) which (24) as potential molecules in asymmetric catalysis and material showed interesting coordination behavior. In the same field, Mo- chemistry, Mamane and Fort used different picolines (25) in the cou- chida’s group designed several ferrocene-containing ligands (18)-(21) pling reaction with racemic (26) or enantiopure ferrocenylacetal (14) by coupling pyrazines, pyrimidines and phenylazoles with the fer- in good yields [26] (Fig. (5)). rocenylzinc complex under palladium catalysis [22, 23, 24]. Chiral Ferrocene-based phosphine ligands are widely used in asymmet- ligands (22) and (23) with ferrocene bridging units for chiral induc- ric catalysis, and during the last decade cross-coupling reactions al- tion in self-assembled helicates were described by Quinodoz and lowed the synthesis of new families of arylphosphinoferrocenes. The colleagues [25]. During their study, they compared the Suzuki and the Negishi coupling was then used with success by several groups in

X Ar Ar O Zn 1) LDA O O S 2) ZnX2 S ArX, Pd S PPh2 Tol Fe Tol Fe Tol Fe Fe

Ar O N Ph2P Ar = Ph 77% N S 3,5-CF3-C6H3 60% O O O

Fe Tol o-MeO-C6H4 90% S S S p-MeO-C6H4 95% Fe Tol Fe Tol Tol (27) 1-Naphtyl 88% Fe

R' (28) 78% (29) 75% (30) 74%

OR OAc RO SOTol Fe SOTol O R = H, MeO, Ac, Bn R' = H, t-Bu S 63-92% Fe Tol Fe HO

(31) (32) 41% Fig. (6). 306 Mini-Reviews in Organic Chemistry, 2008, Vol. 5, No. 4 V. Mamane

CHO O

Fe OMe Fe

Suzuki : 100% O (33) (34) 91% Negishi : 65% S R

S R N hexyl Fe Fe S R N hexyl (35) N (36) hexyl R = H 28% R = phenothiazinyl 20% R = H 38% R = Ferrocene 36% R = phenothiazinyl 54% Fig. (7).

SPh SPh SPh NMe2

Fe Fe Fe Fe

(38) NMe2 (37) Fe 35% (39) 27% 33% SPh

Fe B(OH)2 Ph Ph Fe (40) Excess Excess B(OH) boronic acid 2 porphyrin N N N N + Ph Zn Ph Zn P OTf h N N N N N N Zn Ph Ph N N Ph (42) 18% (43) 14%

Fig. (8). (41) Ph order to introduce an aryle group in -position of a chiral sulfoxide were obtained in good yields. In 1999, Imrie and colleagues reported which served as a directing group and could be easily transformed to a systematic study on the use of Suzuki reaction for the synthesis of a diphenylphosphine group. Pedersen and Johannsen described the monoarylferrocenes from haloferrocenes and arylboronic acids [32]. synthesis of compounds (27), leading after transformation to mono- They found that the use of strong bases such as barium hydroxide or phosphine ligands which showed high catalytic activities in hy- potassium carbonate in the presence of Pd(OAc)2 as a catalyst was drosilylation of styrene [27]. Starting from derivatives (28)-(30), necessary to achieve good conversions. These conditions were later Knochel’s group reported the use of diphosphines and amino- utilized by different groups for the synthesis of ferrocene-containing phosphines in palladium-catalyzed allylic alkylation and amination molecules of potential interest in material chemistry. Mamane and [28, 29]. The sulfoxide group can be maintained in the molecule as Riant obtained an excellent yield of aldehyde (33) in the coupling of a described by Bäckvall’s group in the synthesis of a new class of chiral iodoferrocene compound with p-methoxyphenylboronic acid chiral ferrocene-based quinone ligands (31) and (32). Most of the showing that this method is a good alternative to the Negishi coupling ligands decomposed during the deprotection of the OR groups except [33]. Butler and colleagues generated ferrocenylanthraquinone com- for one (R’ = R = H in (31)) and a poor enantioselectivity was ob- pound (34) in good yield by changing the catalyst to Pd(PPh3)4 [34]. tained when used in the asymmetric diacetoxylation of cyclohexadi- Recently, Sailer and colleagues described several ferrocene- ene [30] (Fig. (6)). phenothiazine systems (35) and (36) with interesting electronic properties [35] (Fig. (7)). 2.2. Suzuki Coupling Other methods involving ferroceneboronic acids have been used The Pd-catalyzed cross-coupling reaction between halobenzenes to perform the Suzuki reaction. Hua and colleagues described the and ferrocene-1,1'-diboronic acid was reported for the first time by coupling between 2,4,6-tris(1’-phenylthio-1-ferrocenyl)boroxin and Knapp and Rahahn [31]. 1,1'-Diphenyl- and 1,1'-bis(halophenyl)- 1,8-diio-donaphtalene to give (37) or 1,8-diidobinaphtyl to yield (38) substituted ferrocenes bearing fluoro, chloro and bromo substituents in presence of Pd(PPh3)4/NaOH system in moderate yields [36]. With Metal-Catalyzed Cross-Coupling Reactions Mini-Reviews in Organic Chemistry, 2008, Vol. 5, No. 4 307

NaOH, MW 57% A number of chiral ferrocenyl ligands having an aryle group di- N R = B(OH)2 rectly attached to one or both Cp rings were developed during the last KOH/Al2O3 57% Fe years. Laufer and colleagues described the synthesis and application R = 4-pyridyl NaOH, Reflux 53% in asymmetric diethylzinc addition to benzaldehyde of a C - R 2 (44) KOH/Al2O3 30% symmetric planar chiral ferrocene diamide (47) [42]. Although the R = 5-pyrimidyl KOH-KF/Al O 20% 2 3 yield of the coupling was low, the ligand was obtained with un- N changed ee (enantiomeric excess) comparing to the starting material. R = B(OH)2 KF/Al2O3 40% N A similar ligand was prepared in a better yield by the Stille coupling Fe R = 5-pyrimidyl KOH/Al2O3 32% but the ee was not determined. Johannsen’s group improved its own synthesis of aryl-ferrocenyl phosphines by using the Suzuki coupling R (45) Fe instead of the Negishi protocol [43]. The new conditions using a SMe chiral ferrocene boronic acid allowed the formation of compounds (48) containing free amino and hydroxyl groups. Anderson and col- FcB(OH)2 leagues reported the preparation and evaluation of ferrocenyloxa- zoline palladacycle catalysts derived from ligands (49) in catalytic NN CuTc, [Pd (dba) , TFP] NN asymmetric synthesis of chiral allylic amines [44]. A new class of B 2 3 cat B ferrocenylphosphines (50) was prepared by Stead and Xiao starting FF 98% FF(46) from ferrocene diboronic acid (40) and bromoarenes bearing a diphenylphosphine oxide group [45]. A subsequent reduction in pres- Fig. (9). ence of HSiCl3 yielded the free phosphines. A series of precursor phosphine ligands (51) containing aryl groups was recently obtained PdCl2(dppf)/NaOH system, Köcher and colleagues obtained a low in high yields by Wang and colleagues [46]. After transformation to yield of (39) by coupling 3,5-(dimethylamino)methyl iodobenzene 1,2,3-trisubstitued ferrocenyl diphos-phines (52) containing a phenyl with ferrocene. Compound (39) was then used for NCN pincer com- or a xylyl group, these ligands were compared to other known plexes synthesis [37]. Ba(OH)2 was used as the base by Cammidge phosphines in asymmetric hydrogenations (Fig. (10)). and colleagues for the synthesis of face-to-face porphyrin-ferrocene systems [38]. It has been shown that changing the ratio between 1,1’- 2.3. Stille Coupling ferrocene diboronic acid (40) and porphyrin (41) modified the reaction pathway. While excess boronic acid delivered the ferrocene- Ma’s groups reported the synthesis of a variety of heteroaryl fer- porphyrin dyad (42) with loss of one boronic acid group, excess por- rocenes by using the Stille cross-coupling. In presence of PdCl (PPh ) as the catalyst, tributylstannylferrocene and electron- phyrin yielded an unexpected product (43) resulting from the in- 2 3 2 poor heteroaryls gave the desired coupling products (53)-(58) with tramolecular cyclization with no incorporation of ferrocene (Fig. (8)). good yields. Less electron-poor substrates required the use of The Suzuki reaction has been applied to the coupling of several Pd(PPh3)4/CuO system to achieve good conversions [47]. With 1,1’- heterocycles with ferrocene mono- or di-boronic acid. During its bis (tributylstannyl)ferrocene (59), only electron-poor heterocycles work on molecular crystal engineering involving organometallics were described to perform efficient stepwise coupling to give (60) building blocks, Braga’s group described the synthesis of pyridine and (61) respectively [48]. The intermediary 1-tributylstannyl, 1’- and pyrimidine ferrocenyl derivatives (44) and (45). Methods such as heteroaryl ferrocenes (60) were also homocoupled in presence of microwaves [39] or KF/alumina [40] in the presence of PdCl2(dppf) copper to yield bis(heterocyclyl)biferrocene compounds (62) [49] as the catalyst were used for the selective preparation of mono-, (Fig. (11)). homo-bis and hetero-bis-functionalized ferrocene starting from 1,1’- In order to perform the cross-coupling between electron-rich and ferrocene diboronic acid (40). A very efficient method for Bodipy sterically demanding partners, methods involving ligands such as functionalization involving a thiomethyl group in the cross-coupling AsPh or Pt-Bu were recently described. Song and colleagues used with boronic acids was reported recently by Pena-Cabrera and col- 3 3 AsPh as ligand for palladium to prepare pyrimidine nucleosides (63) leagues [41]. Bodipy (46) incorporating ferrocene in 8-position could 3 incorporating a ferrocene moiety as a redox probe to study the elec- be prepared by this method with an excellent yield (Fig. (9)). tron transfer in DNA [50]. The same catalyst system was recently

OMe R = Br 54% R = Ph 84% MeO R R = I 45% Ar R = 4-MeOC H 88% O 6 4 R = OH 50% R = 4-CF3C6H4 33% CON(i-Pr) R = OMe 69% R = 2,6-(MeO)2C6H4 20% 2 SO-p-Tol N R = OBn 49% Fe t-Bu R = 1-C10H7 92% Fe Fe R = NH2 33% R = 2-MeC6H4 85% CON(i-Pr)2 (48) R = NHAc 85% (49) R = 2-MeOC6H4 83% (47) 20% R = NO2 78% R = 4-MeSC6H4 76%

POPh2 PPh2 Ph PR2 HSiCl3 Ar Ar O Fe POPh2 Fe PPh2 N PPh2 Fe Fe Ar = Ph 51% 3-position : 54% (50) 4-position : 78% Ar = Xyl 80% (51) (52)

Fig. (10). 308 Mini-Reviews in Organic Chemistry, 2008, Vol. 5, No. 4 V. Mamane

R2 Ph Ph 1 2 R = Me, R = NO2 89% 1 2 R = NO2, R = Me 91% O O 1 2 R = MeO, R = NO2 87% N 1 2 N 1 R = NO2, R = MeO 85% Fe Fe Ph Fe N R R1 = Cl, R2 = NO 80% 2 CO2Et (53) (54) 95% (55) 89% 2-N, R = H 95% R 3-N, R = H 85% 3-N, 6-NO 96% S R = H 80% 2 S R = H 90% N 5-NO 95% 3-N, 6-NHAc 93% 2 R = COMe 78% Fe 3-N, 5-Br 56% Fe 5-COCH3 89% Fe R = COPh 36% R 5-COPh 90% R 3-N, 5-NO2, 6-NH2 90% (58) 3-N, 5-NH2 0% 5-CO-pNO2C6H4 56% (56) (57) 3-N, 5,6-NH2 0%

1 HetAr R2 S 1 SnBu3 HetAr R3 Fe Fe O N N 2 N 1 2 3 SnBu3 SnBu3 R = Me, R = NO2 85% R = COCH3 75% 70% R1 R1 = NO , R2 = Me 83% R3 = COPh 65% (59) (60) 2

R3 = COCH 75% 2 3 From 2-nitropyridine HetAr R3 = COPh 81% Ar1Het HetAr1 HetAr1 S R3 = COCH 65% Fe Fe 3 From 8-methyl-6-nitroquinoline Fe R3 R3 = COPh 78 % HetAr2 R3 = COCH 60% (61) 3 From 6-methyl-8-nitroquinoline (62) 45-96% R3 = COPh 80 % Fig. (11). used by Weber and colleagues for the synthesis of 1,2-disubstituted of ferrocenyl aryl products (67)-(69) in good yields [54]. A nickel- planar-chiral ferrocene ligands (64) [51]. The Pt-Bu3 ligand was assisted intramolecular coupling was used to perform the synthesis of shown to allow an efficient cross-coupling reaction between tributyl-

O N Fe Fe Fe HN R OPh Fe O (66) O N O O Fe N R = Et 80% (71) 45% (70) 47% HO R = Br 5% O O (63) 95% (64) 74% (racemic) Het OH Fe Fe Fe Fe N R

(67) (65) (68) 92% (69) 3-pyridine 84% Fe 14 examples (60-97%) 76% 2-thiophene 90% N Fig. (13). Fig. (12). new chiral aryl-ferrocenyl ligands (70) [55]. A cobalt-catalyzed cross- stannylferrocene and a bromopyridine containing the 2,5-dimethyl coupling reaction involving a ferrocenyl cuprate formed in situ was pyrollidine group to furnish (65) [52] (Fig. (12)). recently described to give (71) [56] (Fig. (13)).

2.4. Miscellaneous 3. OTHER FERROCENE-CARBON BOND FORMATION Ferrocenyl pyridines (66) were prepared in good yields by using 3.1. Ferrocene-Alkyne Bond: the Sonogashira Reaction the nickel-catalyzed Kumada coupling between ferrocenyl Grignard The triple bond spacer is widely used in ferrocene-based materi- intermediates and 4-bromopyridine [53]. The mono-coupling of 1,1’- als because it allows a good electronic communication between the dibromoferrocene was not selective and furnished the desired com- ferrocene unit and other electro-active groups. In this regard, the pound in a poor yield. Bis(ferrocenyl)mercury reagents were coupled Sonogashira reaction is the method of choice to couple alkynes and with aryl iodides in presence of a palladium catalyst to give a variety iodoferrocenes [57]. Metal-Catalyzed Cross-Coupling Reactions Mini-Reviews in Organic Chemistry, 2008, Vol. 5, No. 4 309

OMe OMe

Si(i-Pr) OMe 3 MeO Fe Fe Fe Fe MeO (i-Pr)3Si

Lidner and coll. : 55% (72) 28% MeO (73) OMe Engtrakul and Sita : 42%

Fe Fe t-BuS MeO St-Bu (74) 26%

NMe2

Me2N Pc Fe NMe2 Fe Pc = Phthalocyanine I

Me2N (75) 9% (76) 48%

Fig. (14).

SiMe3 Co (CO) 2 8 Fe Fe Fe 2nd Me Cobalt complexes Me Me3Si S st 1 n = 0, 1 Fe CH2 st nd S n (77) n = 0 1 step: 25%; 2 step: 23% n = 1 1st step: 11%; 2nd step: 22% Me Me (78) Me Me Co (CO) CHO 2 8 OH OH Fe Co2(CO)8 OH Fe Me Me

70% Fe (79) (80) HO Me Me 2-CHO, (RFc) : 70% ; 2-CHO, (SFc) : 77% Co2(CO)8 3-CHO, (RFc) : 90% ; 2-CHO, (SFc) : 60% Fig. (15).

Plenio and colleagues described the synthesis of several optically [63]. In this last case the obtained mono-coupling product (76) was and redox-active ferroceneacetylene polymers and oligomers such as reused in a second Sonogashira reaction but again the bis- derivative (72) [58]. While the reaction is high yielding with 1-iodo, phthalocyanine ferrocene derivative was not formed (Fig. (14)). 2-substituted ferrocene derivatives, the yield dropped when using The alkyne functionality was used respectively by Robinson’s 1,1’-dioodoferrocene. The main reason could be the steric hindrance and Woods’ groups as a ligand for cobalt complexes. In the first case, generated after the first coupling. Lindner and colleagues [59], and it was shown that polyferrocenes in (77) can serve as a communicator recently Engtrakul and Sita [60] noted that the solubility of the result- linkage between Co (CO) dppm units [64]. In the second application, ing compounds was of major importance for the bis-coupling success. 2 4 new ferrocenophane derivatives (78) and (79) bearing two The presence of methoxy and tri-isopropylsilyl groups in the alkyne Co (CO) (alkyne) complexes were isolated and studied by electro- moiety allowed the formation of -extended molecules (73) in good 2 8 yields. Moderate yields were reported by Ma and colleagues by using chemistry [65]. Jaouen’s group showed that the alkyne group can tert-butylsulfanyl groups in the substrates for the synthesis of (74), a serve as a linker between chiral ferrocene and oestradiol through the precursor for symmetrical molecular wires [61]. A low yield of bis- synthesis of (80) [66] and that the estrogen receptor was capable to product (75) was obtained by Köcher and colleagues during the recognize preferentially one diastereoisomer [67]. During this work, preparation of 4-ferrocenyl-NCN pincer complexes [62], whereas no the authors noted that the Sonogashira coupling was more efficient expected product was isolated by Gonzalez-Cabello and colleagues with iodoferrocene compounds, whereas the Stille coupling was more 310 Mini-Reviews in Organic Chemistry, 2008, Vol. 5, No. 4 V. Mamane

Fe R1 2 R2 R = H 40% R2 = 2-indene 47% ZnCl (81)

Fe 2-bromo-indene Me2N R2 Pd cat

R2 = H or ZnCl Fe R2 R2 = H 74% 2 (82) R = 2-indene 26%

R = CONEt2 69%

R R OCOCN O CH2=CHSnBu3 R = 85% Fe Fe I Pd cat R = OCOCN 82% (83) Fig. (16).

O R2 3.2. Ferrocene-Alkene Bond CONR2 COCONR2 OMe Two recent examples described the formation of a ferrocene- Fe Fe N alkene bond on the basis of cross-coupling reaction. A Negishi cou- R R R1 O pling was used by Anderson and colleagues to introduce one or two (84) (85) Fe indenyl ligands on the ferrocene to give (81) and (82) [69]. 1- R = H 71-88% R = H 57-72% Substituted, 1’-vinylferrocenes (83) were prepared in good yields by (86) 75-94% R = CONR2 70-92% R = I 11-40% Szarka and colleagues by a Stille coupling in presence of vinyltribu- 14-35% R = I O R2 tyltin [70] (Fig. (16)). O R1 O OMe N 3.3. Ferrocene-CO Bond: Aminocarbonylation N OMe R1 O The aminocarbonylation reaction of iodoferrocene compounds Fe catalyzed by palladium was intensively used by Skoda-Földes’ group O R2 R1 O Fe for the synthesis of amides (84) and -ketoamides (85) [70-72]. The N reaction was described to proceed with both 1-iodoferrocene and (87) 26-89% OMe (88) 1,1’-diiodoferrocene with moderate to good yields. A nice entry to O R2 27-47% ferrocenyl amino acid derivatives (86)-(88) was also described by R = Et, n-Bu, -(CH2)5-, -(CH2)2-O-(CH2)2 using protected amino-acids as the amine partners in the reaction [73, Amino acids : Gly-OMe, L-Ala-OMe, L-Phe-OMe, L-Met-OMe, L-Pro-OMe 74] (Fig. (17)).

Fig. (17). 4. FERROCENE-HETEROATOM BOND FORMATION practical for other iodocyclopentadienyl complexes (Mn, Re). The Only a few examples described the direct formation of a fer- explanation for these interesting observations was reported recently rocene-heteroatom bond. Copper in catalytic or stoechiometric by Amatore and colleagues [68] (Fig. (15)). amounts is generally preferred to effect these transformations. For the

O R = H I R = I N NH 3 NH2 2 NaN H , Pd/C Hydrazine N Cu-Phthalimide Fe 3 Fe 2 Fe Fe 99% Fe 82% R 59% N3 77% NH2 O (90) R2 (89)

N X Y N NPh2 N N N X X Y Fe Fe Fe Fe X = CH, N Fe R1 1 2 X, Y = CH, N N R , R = H, Me, NO2 X, Y = CH, N (91) N 31-84% (92) 43% (93) 50% (94) 35-95% (95) 28-96% Fig. (18). Metal-Catalyzed Cross-Coupling Reactions Mini-Reviews in Organic Chemistry, 2008, Vol. 5, No. 4 311 preparation of 1,1’-diaminoferrocene (89) and 1-aminoferrocene (90), [8] Guillaneux, D.; Kagan, H. B. J. Org. Chem., 1995, 60, 2502-2505. improved procedures were reported. Shafir and colleagues described [9] Ferber, B.; Kagan, H. B. Adv. Synt. Catal., 2007, 349, 493-507. [10] Helberg, F. L.; Rosenberg, H. Tetrahedron Lett., 1969, 10, 4011-4012. the synthesis of (89) in two steps from the readily available 1,1’- [11] Lee, M.-T.; Foxman, B. M.; Rosenblum, M. Organometallics, 1985, 4, 539- dibromoferrocene [75]. Heinze and Schlenker obtained (90) in good 547. yield and purity by reacting iodoferrocene with a pre-formed Cu- [12] Hudson, R. D. A.; Foxman, B. M.; Rosenblum, M. Organometallics, 2000, phtalimide complex following by deprotection [76]. Recently, Bolm’s 19, 469-474. [13] Malessa, M.; Heck, J.; Kopf, J.; Garcia, M. H. Eur. J. Inorg. Chem., 2006, group described the direct synthesis of N-substituted ferrocenes (91)- 857-867. (93) using stoechiometric amount of CuI in DMSO [77]. A catalytic [14] Barlow, S.; O’Hare, D. Chem. Rev., 1997, 97, 637-669. protocol for the Ulmann-type coupling was then reported by Na- [15] Ogawa, S.; Muraoka, H.; Sato, R. Tetrahedron Lett., 2006, 47, 2479-2483. garkar’s group for the efficient preparation of a range of N-substituted [16] Yu, Y.; Bond, A. D.; Leonard, P. W.; Vollhardt, K. P. C.; Whitener, G. D. Angew. Chem. Int. Ed., 2006, 45, 1794-1799. ferrocenes (94) and (95) [78] (Fig. (18)). [17] Yu, Y.; Bond, A. D.; Leonard, P. W.; Lorenz, U. J.; Timofeeva, T. V.; Vol- Plenio’s group reported the copper-catalyzed synthesis of fer- lhardt, K. P. C.; Whitener, G. D.; Yakovenko, A. A. Chem. Commun., 2006, 2572-2574. rocenyl aryl ethers (96)-(98) from iodo-and bromo-ferrocenes in [18] Mamane, V.; Gref, A.; Lefloch, F.; Riant, O. J. Organomet. Chem., 2001, moderate to good yields [79]. 2,2,6,6-Tetramethylheptane-3,5-dione 637-639, 84-88. (TMHD) was found to be an efficient ligand for copper when this [19] Mamane, V.; Gref, A.; Riant, O. New J. Chem., 2004, 28, 585-594. reaction was carried out in N-methylpyrrolidinone (NMP) solvent [20] Mamane, V.; Ledoux-Rak, I.; Deveau, S.; Zyss, J.; Riant, O. Synthesis, 2003, 455-467. using Cs2CO3 or K3PO4 bases. During their study on the palladium- [21] Enders, M.; Kohl, G.; Pritzkow, H. J. Organomet. Chem., 2001, 622, 66-73. catalyzed asymmetric phosphination of iodoarenes, Blank and col- [22] Horikoshi, R.; Nambu, C.; Mochida, T. Inorg. Chem., 2003, 42, 6868-6875. leagues reported one example using iodoferrocene [80]. Product (99) [23] Mochida, T.; Okazawa, K.; Horikoshi, R. Dalton Trans., 2006, 693-704. was obtained in quantitative yield but in low ee (Fig. (19)). [24] Mochida, T.; Shimizu, H.; Suzuki, S.; Akasaka, T. J. Organomet. Chem., 2006, 691, 4882-4889. [25] Quinodoz, B.; Labat, G.; Stoeckli-Evans, H.; von Zelewsky, A. Inorg. Chem., 2004, 43, 7994-8004. R [26] Mamane, V.; Fort, Y. J. Org. Chem., 2005, 70, 8220-8223. R [27] Pedersen, H. L.; Johannsen, M. J. Org. Chem., 2002, 67, 7982-7994. [28] Lotz, M.; Kramer, G.; Knochel, P. Chem. Commun., 2002, 2546-2547. O [29] Kloetzing, R. J.; Knochel, P. Tetrahedron Asymmetry, 2006, 17, 116-123. O [30] Cotton, H. K.; Huerta, F. F.; Bäckvall, J.-E. Eur. J. Org. Chem., 2003, 2756- Fe R' 2763. Fe [31] Knapp, R.; Rehahn, M. J. Organomet. Chem., 1993, 452, 235-240. O [32] Imrie, C.; Loubster, C.; Engelbrecht, P.; McCleland, C. W. J. Chem. Soc. Perkin Trans. 1, 1999, 2513-2523. (97) R, R' = H, Me, t-Bu [33] Mamane, V.; Riant, O. Tetrahedron, 2001, 57, 2555-2561. (96) R = H, Me, t-Bu, Cl [34] Butler, I. 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Received: March 25, 2008 Revised: May 12, 2008 Accepted: May 12, 2008