Tebbe-like and Phosphonioalkylidene and -alkylidyne Complexes of Scandium.

The bonding between scandium and carbon in a series of alkylidene- and alkylidyne-like moieties is compared. The Tebbe analogue complex (PNP)Sc(μ-CHSiMe)(μ-CH)[Al(CH)(CHSiMe)] () (PNP = N[2-PPr-4-methylphenyl]) could be formed by adding AlMe to (PNP)Sc(CHSiMe) (). The fluxional behavior of is studied by a combination of 2D C-H HMQC, HMBC, and other heteronuclear NMR spectroscopic experiments. The phosphonioalkylidene complex (PNP)Sc(CHPPh)(CH) () could be prepared from by treatment with 2 equiv of the ylide HCPPh or by methane elimination from (PNP)Sc(CH) and 1 equiv of HCPPh. The reactivity of the alkylidene in was further explored with NAd, which gave insertion at the Sc-C bond, yielding (PNP)Sc(CH)[η-NAdCHSiMeAl(CH)(CHSiMe)] (), while DMAP provided C-H activation across the alkylidene with loss of the Al-C bond to form (PNP)Sc(η-NCHNMe)(CHSiMe) (). Utilizing the same approach that yielded , methane elimination in could further be promoted with Al(CH) to furnish the first example of a scandium phosphonioalkylidyne complex, (PNP)Sc(μ-CPh)(μ-CH)Al(CH) (). Experimental and theoretical studies were combined to compare the bonding in , , and , in order to understand the legitimacy of Sc-C multiple bond character.