Tertiary silanes

We also reported that CpFe(CO)2Me acts as a precursor for the Si-O-Si bond formation reaction from hydrosUane and DMF (Scheme 51)[ 166,167]. In this reaction, tertiary silanes and bis(silyl) compounds are converted into the corresponding disUox-anes and the polymers with (-R-Si-O- i)n backbone, respectively. 

Hydride species were also formed in the dehydrogenative coupling of hydrosilanes with DMF [45]. The catalytic system is applicable to tertiary silanes, which are known to be difficult to be converted into disiloxanes (Fig. 17). The catalytic reaction pathway involves the intermediacy of a hydrido(disilyl)iron complex... 

Itazaki M, Ueda K, Nakazawa H (2009) Iron-catalyzed dehydrogenative coupling of tertiary silanes. Angew Chem Int Ed 48 3313-3316... 

There are relatively few examples of the reaction of platinum(O) with tertiary silanes. A novel example is the reaction of [Pt(PEt3)4] with the rhodium complex [RhCl(H)(SiAr3)(P(Pr1)3)2], which results in silane transfer to give the platinum(II) complex cis- [PtHtSiArsXPCPr1) ].64... 

Other cationic Ir(I) complexes containing the bidentate ligands, such as bis(l-pyrazolyl)methane (BPM) and bis(3,5-dimethyl-l-pyrazolyl)methane (dmBPM), that is [Ir(BPM)(CO)2] [BPli4p and [Ir(dmBPM)(CO)2] BPh4]T were also reported to be effective catalysts for the alcoholysis of binary and tertiary silanes [77]. 

Widenhoefer and co-workers have developed an effective protocol for the asymmetric cyclization/hydrosilylation of functionalized 1,6-enynes catalyzed by enantiomerically enriched cationic rhodium bis(phosphine) complexes. For example, treatment of dimethyl allyl(2-butynyl)malonate with triethylsilane (5 equiv.) and a catalytic 1 1 mixture of [Rh(GOD)2] SbF6 and (i )-BIPHEMP (5 mol%) at 70 °G for 90 min gave the silylated alkylidene cyclopentane 12 in 81% yield with 98% de and 92% ee (Table 4, entry 1). A number of tertiary silanes were effective for the rhodium-catalyzed asymmetric cyclization/hydrosilylation of dimethyl allyl(2-butynyl)malonate with yields ranging from 71% to 81% and with 77-92% ee (Table 4, entries 1-5). Although the scope of the protocol was limited, a small number of functionalized 1,6-enynes including A-allyl-A-(2-butynyl)-4-methylbenzenesulfonamide underwent reaction in moderate yield with >80% ee (Table 4, entries 6-8). 

Dehydrogenative silylation has also been observed for terminal alkyne substrates. Doyle and co-workers reported in 1991 that a small amount (6%) of alkynylsilane was observed in the product mixture that results from reaction of phenylacetylene and Et3SiH catalyzed by Rh2(pfb)4.41 The remaining components of the product mixture resulted from hydrosilylation. Crabtree and co-workers have found that in reaction of terminal alkynes with various tertiary silanes, dehydrogenative silylation can become the predominant route, depending on reaction conditions [Eq. (7)].42... 

The Corey group has reported that Cp2TiCl2/nBuLi effectively catalyzes the high yield alcoholysis of primary, secondary, and tertiary silanes with a variety of alcohols under mild reaction conditions.160 All Si-H functionalities are replaced with alkoxy groups in reactions of ethanol and phenol, although increased temperatures and/or reaction times are required for highly substituted hydrosilanes. The system also appears to be influenced... 

The manganese complex, Ph3SiMn(CO)5 has been used to promote hydrosilylation of olefins both thermally and photochemically. With HD4 and pentene, and 0.1 mol% of Ph3SiMn(CO)5, thermal activation gave a 20% yield of D4-D4 but none from photochemical activation.109 A few complexes of iron, Fe(CO)5,110a Fe(CO)2 P(OPh)3]2H(SiMe2Ph),110b and Fe(dppe)2(CH2=CH2)ul have been reported to couple tertiary silanes but few details are available. 

Ph3P)CuH]6 did not catalyze reaction of Et2NH with secondary and tertiary silanes.145 This is not surprising in view of the results of Liu and Harrod, who showed that CuCl, or CuH catalysts do not activate the second N—H of primary amines, or the third N—H bond of NH3, toward reaction with silanes.147148... 

Liu and Harrod ° reported on dehydrocoupling of ammonia and silanes catalyzed by dimethyltitanocene. Tertiary silanes, for example, Ph2SiMeH, were transformed into disilazanes. Yet no polysilazanes could be obtained when reacting PhSiH3 under similar conditions. Homodehydrocoupling (which proceeds with Si-Si linking compare Scheme 18.3) effectively competed with amination reactions, indicating that the products obtained by ammonolysis of PhSiHj are polyaminosilanes [SiPh(NH2)] rather than polysilazanes [SiPhH-NH] . 

The condensation of secondary silanes requires more rigorous conditions and no catalyst has yet been reported to couple tertiary silanes efficiently [140]. The great interest in polysilane polymers and their potential application come from their unusual electronic, optical, and chemical properties [142], particularly as preceramic materials [143]. The reaction constitutes the only alternative to Wurtz coupling for the formation of silicon-silicon bonds. 

We have previously shown that the mononuclear zirconium hydride complexes 1 activate, under very mild conditions, the C-H bond of alkanes, including methane [7], The mechanism involves a four center intermediate, as proposed earlier for electrophilic activation of C-H bonds by group 3, 4 and lanthanides d° complexes [8], Given the similarities of the energies of dissociation of C-H and Si-H bonds, it is not surprising at ail that activation of Si-H bonds occurs with 1. Reactions of H/D exchange, followed by in situ IR spectroscopy, reveal that all types of silanes are activated, i.e. primary, secondary and even tertiary silanes [9],... 

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