Gi. Nikonov et al., FACILE INSERTION OF CIPPH2 INTO NB-H BONDS AS A SYNTHETIC ROUTE TO NEW PHOSPHINO AND PHOSPHIDO DERIVATIVES OF NIOBOCENE, Organometallics, 13(8), 1994, pp. 3127-3133
Synthetic approaches to phosphorus derivatives of niobocene) including
a metathesis of Cp2NbH2Li with ClPPh2 and insertion of ClPPh2 into th
e Nb-H bond, were studied. The smooth reaction of Cp'2NbH3 (a, Cp = C5
H5; b, Cp' = C5H4Me) with ClPPh2 affords [Cp'2-NbH2PHPh2]Cl (3a,b) in
high yield. Deprotonation of 3 leads exclusively to Cp'2NbH(PHPh2) (2)
, while the isomeric complex Cp'2NbH2PPh2 (1) was not observed; it see
ms to be the intermediate precursor to complex 2. Direct reaction of C
P2NbH2Li with ClPPh2 also gives 2a but in poorer yield. 2 was found to
selectively rearrange into Cp'2Nb(PHPhC6H4-) (5), the first ortho-met
alated phosphine complex of the early transition metals. The formulati
on of 5 was supported by H-1, C-13, and P-31 NMR spectroscopy. However
, X-ray diffraction study was not possible due to twinning problems. B
y repeated insertion of ClPPh2 into the Nb-H bond of 2, followed by de
protonation, we obtained [Cp'2Nb(PHPh2)2]Cl (7) and (C5H4-Me)2NbPPh2(P
HPh2) (8b). Deprotonation of 7 and 8b affords a new niobocene anionic
complex CP'2Nb(PHPh2)2M (M = Na, Li (9)). Thermal degradation of 2, 8,
and 9, leading to 5, was studied and found to proceed via an intermed
iate Cp'2NbPPh2 (6) which was identified by NMR spectroscopy.