Bis silylene

Donor-bridged bis(silylene) complexes (Equation (4)) are now known for all the group 6 metals.72-74 For example, when CpCr(CO)3 is photolyzed with HSiMe2SiMe2OMe, the product is 26 (M = Cr X = OMe). Structural data for members of this family show that the four-membered ring is folded (internal dihedral angle for 26 with M=Cr, X = OMe is 162.4°), and this is attributed to steric repulsion between CO and silicon-bound Me groups. The fluxional... 

Addition of a persistent silylene (see Section V.III.C) to nickel carbonyl resulted in the first bis-silylene transition metal complex without Lewis base stabilization... 

Silylene 59 also behaves somewhat like a phosphine in its interactions with metal carbonyls98,149-376. Typical reactions involve substitution of silylene for CO, to give a silylene-metal complex. Three examples are shown in Scheme 20, and the structure of the nickel complex 75 is displayed in Figure 7149. This complex is both the first silylene-nickel complex, and the first example of a bis-silylene-metal complex free of stabilization by Lewis base donors. 

For the Z-to-E isomerization, a mechanism via silylsilylene complex 238 [Eq. (112)] has been proposed. Mechanisms including the following processes are excluded on the basis of the theoretical calculations (1) dissociation-association equilibrium between the corresponding disilene and Fe(CO)4, (2) removal of one CO from 236Z and then Si-Si bond cleavage forming the corresponding bis-silylene... 

Bis(silylene) complexes with iron, 3, 528 with osmium, 3, 532... 

Routine MS data are available for 1,3,2( A2)-diazasiloles 83, 85, 89, and 90. Using electron impact methods the positive M+ ion was detected in 35-64% relative abundance <1994JA2691, 1995CC1931, 1996JOM211, 1998CEJ541>. In the case of the bis-silylene 86 the molecular ion was obtained as the base peak <2005ZFA1383>. Similarly, chemical ionization of compound 87 resulted in the detection of the molecular ion as the most abundant peak <1998ZFA295>. 

An X-ray crystal structure has been determined for 7 and is shown in Fig. 3. This compoimd is the first silylene complex of nickel, as well as the first bis-silylene metal complex of any kind without base stabilization [20]. 

A 93% yield of a unique bis-silylene complex is obtained when a cyclic diaza derivative is combined with a metal carbonyl (b). 

Some reports of silylene complexes have appeared, but many of these involve incomplete characterization or have subsequently been disproved. One problem is that the presence of a M=Si double bond is difficult to establish unequivocally with spectroscopy. The product in equation 51 was formulated as the monomeric bis(silylene) complex... 

Variation of the Substituent R in Bis(silylene)amido-Bridged Metallocene Complexes of the Type (Cp-SiMe2-NR-SiMe2-Cp)ZrCl2... 

M. Denk, R. K. Hayashi, and R. West,/. Chem. Soc., Chem. Commun., 33 (1994). Silylene Complexes from a Stable Silylene and Metal Carbonyls Synthesis and Structure of [Ni(t-Bu—N—CH=CH—N—f-Bu)2(CO)2), a Donor-Free Bis-Silylene Complex. 

The reaction of the bis(silylene)-ruthenium complex [Ru / (3 /,3 /)-(SiMe2)20Me Gp(PPh3)] 183 with methanol affords the hydrido-bis(silyl)-Ru(iv) derivative 186 which, in the presence of a large excess of methanol, is slowly... 

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