AMINE-INDUCED COUPLING OF CARBONYL AND NITRILE LIGANDS IN TUNGSTEN(II) COMPLEXES

Reaction of [Tp'(CO)3W(N=CMe)][BF4] (1), an intermediate formed in situ from Tp'W-(CO)3I and AgBF4 in acetonitrile, with ammonia or n-butylamine generates neutral complexes of the type Tp'(CO)2W-C(=O)-N(R)-C(Me)=N(H) (R = H (2), n-butyl (3)). Protonation of these heteroatom metallacycle complexes occurs at the acyl oxygen atom to produce cationic metallacycle hydroxycarbene complexes, [Tp'(CO)2W=C(OH)-N(R)-C(Me)=N(H)][BF4] (R = H (4), n-butyl (5)). NMR spectra and a single crystal X-ray structure indicate that the five-membered ring is planar and effectively lies in the molecular mirror plane with the carbene carbon adjacent to the two terminal carbonyl ligands. Methylation of the metallacycle acyl complexes at the acyl oxygen produces analogous cationic metallacycle methoxycarbene complexes of the type [Tp'(CO)2W=C(OMe)-N(R)-C(Me)=N(H)][CF3SO3] (R = H (6), n-butyl (7)). Reaction of the [Tp'(CO)3W(N=CMe)][BF4] intermediate with the bulky tert-butylamine nucleophile results in formation of an unusual amido complex, Tp'(CO)2W-N-C(=CH2)-N(Bu(t))C(=O) (8), with the original nitrile nitrogen now three-coordinate and bound to the metal and both carbons of the four-membered ring. Donation of the lone pair of electrons on the nitrogen of the amido ligand to the tungsten center is reflected by the low IR stretching frequencies of the carbonyl ligands and their downfield carbon resonance in the C-13 NMR. NMR spectra and an X-ray structure indicate that the planar four-membered, ring of the amido ligand lies on the molecular mirror plane.