SYNTHESIS AND STRUCTURE OF THE NIOBIUM(III) PHOSPHIDO COMPLEX (C5H5)2NB(CO)(PIPRPH) - EFFICIENT GAUCHE EFFECT AND LOW INVERSION BARRIER IN BENT-METALLOCENE CHEMISTRY

Reaction of Cp2Nb(CO)H with P(i)PrPhCl afforded the ionic product [Cp2Nb(CO)(P(i)PrPhH)]Cl, which upon treatment with NaOH gives the neutral niobium phosphido complex Cp2Nb(CO)(P(i)PrPh) (1). 1 crystallizes in the monoclinic space group P2(1)/c, with a = 16.899 (3) angstrom, b = 15.409 (2) angstrom, c = 13.717 (3) angstrom, beta = 90.94 (2)-degrees, V = 3571.2 angstrom 3, Z = 8, and R = 0.038, with two independent chiral molecules in the asymmetric unit of the unit cell. One of them is related to the other by rough translation by a half of the lattice vector a. The torsion angles in both molecules involving the metal and the phosphorus lone pairs are close to 73-degrees, thus indicating an efficient operation of the ''gauche effect''. The origin of the observed low inversion barrier at phosphorus is discussed.