STRUCTURE OF [(1,2-ETA-2)-1,3,5,7-CYCLOHEPTATETRAENE]BIS(TRIPHENYLPHOSPHINE)PLATINUM(0)

[Pt{(1,2-eta-2)-C7H6}{P(C6H5)3}2], (I), M(r) = 809.82, monoclinic, P2(1)/c, a = 13.664 (7), b = 16.783(8), c = 16.702(8) angstrom, beta = 111.68(4)-degrees, V = 3559 (3) angstrom3, Z = 4, D(x) = 1.51 g cm-3, lambda(Mo K-alpha) = 0.71069 angstrom, mu = 41.00 cm-1, F(000) = 1608, T = 298 K, R = 0.0329 and wR = 0.0366 for 3807 reflections [I greater-than-or-equal-to 3-sigma(I)]. The Pt atom is involved in asymmetric bonding with the C and P atoms. Pt-C(1) is shorter than Pt-C(2) [2.000 (7) and 2.111 (8) A]. This difference in bond lengths is the result of a difference in the bonding environments around the two C atoms. C(1) is slightly more electronegative than C(2) owing to an extra pi-bond around C(1). Consequently, C(1) exerts a slightly stronger trans effect than C(2) by lengthening bond Pt-P(2) [2.299 (2) angstrom compared to 2.287 (2) angstrom for Pt-P(1)]. The Pt atom lies in the plane of coordination which forms an angle of 131.5 (6)-degrees with the plane of atoms C(1)-C(2)-C(3)-C(7). The torsion angle H(2)-C(2)-C(3)-H(3) is 83 (8)-degrees, close to 90-degrees, and therefore no coupling was found between H(2) and H(3) in 2D (COSY) H-1 NMR [Winchester & Jones (1985). Organometallics, 4, 2228-2230]. This study not only confirms the allene form (1) rather than the carbene form (2) for the Pt complex of C7H6 in the solid state as well as in solution, but the torsion angle of nearly 90-degrees between H(2) and H(3) explains why they are virtually uncoupled in the H-1 NMR spectrum.