Carbene complexes selenium-stabilized

The synthesis of metal complexes of type 213 can be performed by reacting metal-carbene complexes with selenium sources such as alkyneselenolates 203.430 Also the stability of unstable selenocarbonyl compounds such as selenoaldehydes can be enhanced by coordination to metal carbonyls and the reactivity of such complexes has been studied. Complex 216 can react with methylthiohexyne and the product is a different complex 217 with the selenium atom still coordinating to the metal carbonyl fragment (Scheme 66).431... 

One of the synthetic procedures of metal complexes of type 53 is the reaction of metal-carbene complexes with selenium sources such as alkyneselenolates [109]. The stability of selenobenzaldehyde is enhanced by coordinating to metal carbonyls, and the reactivity of the complexes has been studied [110]. For example, the selenobenzaldehyde complexes reacts with methylthiohexyne even at - 30 °C to afford another type of complex where the selenium atom of the selenocarbonyl group is still coordinated to the metal (Eq. 29) [llOd]. 

To date there have been no reported complexes of NHCs to oxygen centers and only one to a sulfur center. This is certainly due to the reactivity of the atoms involved and the tendency to form lu-ea or thiourea derivatives. The NHC-suliur complex was generated from a frustrated Lewis pair reaction of elemental sulfur, giving an NHC-S-B(C6p5)3 complex the selenium analog was also prepared [265]. There have been structures of carbene-alcohol complexes reported however, the coordination occurs between a carbon and a hydrogen via a hydrogen bond [266]. A/]Af-Diamidocarbenes have been exploited in the homonuclear bond-activation of peroxides, disulfides, bromine (vide infra), and even some C—C bonds in diones and cyclopropenones as mentioned earlier [174]. Cyclo-propenyl-l-ylidene-stabilized S(II), Se(II), and Te(II) mono- and dications have also been prepared and characterized [267]. 

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