LIGAND ELABORATION MEDIATED BY A CP-ASTERISK-W(NO) TEMPLATE - STEPWISE INCORPORATION OF SMALL MOLECULES INTO A TUNGSTEN VINYL FRAGMENT

Thermolysis of the alkyl vinyl complex CpW(NO)(CH2SiMe3)(CPh=CH2) (1) in the presence of unsaturated, heteroatom-containing compounds such as esters and nitriles quantitatively affords metallacyclic products o f reductive coupling. These are trapped as 18e complexes via either in tramolecular rearrangement or intermolecular reaction with added trapp ing reagents. The nature of these metallacycles is consistent with the intermediacy of the acetylene complex CpW(NO)(eta(2)-CPh=CH) (A) der ived in situ from the reductive elimination of SiMe4 from 1. With este rs ROAc (R = Me, Et), reductive coupling and C-O bond cleavage yields the alkoxide-containing oxametallacyclopentadiene complexes CpW-(No)( eta(2)-O=C(Me)CH=CPh)(OR) (2, R = Me; 3, R = Et). Thermolysis of 1 in RCN (R = Me, Et, Pr-i) containing small excess amounts of R'OH yields the respective hydroxide or alkoxide compounds CpW(NO)(eta(2)-NH=C(R) CH-CPh)(OR') (4, R = Me, R' = H; 5, R = Et, R' = H; 6, R = Pr-i, R' = H; 7, R = Me, R' = C3H5) Utilization of cyclopentadiene (CpH) as the t rapping agent in MeCN affords the aminopentafulvene complex CpW(NO)(H NC(=C(C4H4))(Me))(eta(2)-NH=C(Me)CH=CPh) (8). VT H-1 NMR spectroscopy reveals the fluxional solution behavior of the fulvene ligand in 8. Th ermolysis of 1 in RCN (R = Me, Pr-i) containing trace amounts of aceto ne gives the bicyclic species CpW(NO)(eta(3)-OC(Me)(2)N=C(Me)CH=CPh) (9, R = Me; 10, R = Pr-i). In the absence of added trapping reagent, t hermolysis of 1 in RCN (R Me, Et) yields the vinyl amidinate complexes CpW(NO)(eta 3-NHC(R)=NC(=C(R-1)(R-2))CH=CPh) (11, R = Me, R-1 = R-2 = H; 12, R = Et, R-1 = H, R-2 = Me). The molecular structures proposed for 2, 4, 8, and 10 are confirmed by single-crystal X-ray analyses. M echanistic proposals to account for the observed chemistry are corrobo rated by the results of labeling studies, while a kinetic study of the transformations yielding 3, 4, and 11 implicates the rate-limiting ge neration of acetylene intermediate A. A qualitative orbital overlap ra tionale is proposed to account for the observed chemistry.