Disilene-metal complexes

The chemistry of silylene-metal complexes has developed in quite another direction, however, from reactions of disilyl-metal complexes, leading to complexes of otherwise unstable disilenes such as Me2Si=SiMe2. Molybdenum and tungsten complexes have been particularly well investigated by Berry and co-workers,103 and platinum complexes have also been isolated.104 Readers interested in this field are directed to a 1992 review of silylene, silene, and disilene-metal complexes.105... 

Reactions of disilenes to form transition metal complexes have hardly been investigated complexes are reported only for platinum. An example is shown in Eq. (35). The Pt complex 76 was identified spectroscopically and from trapping products, but it was a minor product in the reaction and crystals could not be obtained.102... 

The chapter table of contents contains subjects that were either unknown or merely distant hopes a decade ago, such as persistent silylenes, the dissociation of disilenes to silylenes and terminal silylene-transition metal complexes. The kinetics and spectroscopy of silylenes and theoretical treatments of silylene structure and reactivity have made such gigantic strides in the intervening years that they represent new vistas in our understanding. 

The first disilene-group-4 metal complex, disilene-hafnium complex 240, is synthesized using a similar reaction to those shown in Eqs. (108) and (109) [Eq. (113)].153 The reaction of 240 with trimethylphosphine gives the phosphine adduct 241 [Eq. 

Stable transition-metal complexes of tetramesityldisilene result upon irradiation with oxalato bis(tertiary phosphine) complexes of platinum87. The latter photofragment with loss of C02 to yield the 14-electron intermediate (R3P)2Pt, which then apparently adds to the disilene to yield 33 (R = Et or Ph) (equation 30). The two complexes were isolated in the form of air-sensitive orange-red oils and characterized by NMR and mass spectra. The structure of the triethylphosphine derivative was further secured by addition of methanol across the Pt-Si bond. 

Terminally metallated methyloligosilanes result from the appropriate a,o>-dichIcnrkfe, while photolysing Cp(CO)2FeSiMe7SiMe2X (X=H, Me or CgH4Y) gives the suspected disilene-Fe complex (X=H), the silylene complex (X=Me), while for X=Aiyl, the expelled... 

The chemistry of the disilenes (disilaethenes) has developed very rapidly since the discovery of stable compounds. It was an obvious challenge to explore also the possibility of a n-coordination of disilenes to transition metals. According to the Dewar-Chatt-Duncason bonding model, a high stability for a disilene complex should result. 

Major advances in organometallic chemistry during the last years have been achieved in the area of silicon-metal multiple bonding and silicon with low coordination numbers. For late transition metals, new complexes have been synthesized such as silanediyl (A), silene (B), silaimine (C), disilene (D), silatrimethylenemethane (E), silacarbynes (F), cyclic silylenes (G), silacyclopentadiene (H) and metalla-sila-allenes (I) (Figure 3). 

The NMR resonances for the central 29Si nuclei of tetrakis(trialkylsilyl)disilene complexes in solution vary from —160 ppm for 241 to 127 ppm for 240, depending on the bonding characteristics of the disilene ligands to the metals for reference, the 29Si NMR resonances for hexakis(trialkylsilyl)cyclotrisilanes and free disilene 22 are... 

In spite of the presence of usually bulky substituents at the silicon atoms, the Si—Si bond lengths are dramatically shortened and approach those of disilenes. This bond shortening is accompanied by a planar or almost planar arrangement of the substituents R1, R2 and the other silicon atom about each silicon atom. Such a geometrical arrangement resembles the bonding situation in transition metal-olefin complexes which, according to the model... 

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