RAPID INVERSION AT PHOSPHORUS IN THE [ETA(4)-(C6H11)(3)SNP7W(CO)(3)](2-) AND [(EN)(CO)(3)W(ETA(1),ETA(4)-P-7)M(CO)(3)](3-) IONS WHERE M=CR,W

Ethylenediamine ten) solutions of [eta(4)-P7M(CO)(3)](3-) ions [M = Cr (la), W (Ib)l react with (mesitylene)W(CO)(3) to form the bimetallic complexes [(en)(CO)(3)W(eta(1),eta(4)-P-7)M(CO)(3)(3-) where M = Cr (3 a), W (3b) in good yield. Compound 3b can be prepared directly from P- 7(3-) and 2 equiv of (mesitylene)W(CO)(3). Compound 3a reacts with 1 e quiv of P-7(3-) to form la and Ib. En solutions of Ib react with 1 equ iv of (C6H11)(3)SnCl to give [eta(4)-(C6H11)(3)SnP7W(CO)(3)]2(-) (4) i n good crystalline yield as the [K(2,2,2-crypt)(+) salt. The X-ray str ucture of the [K(2,2,2-crypt)](+) salt 3b revealed a norbomadiene-like P-7 cage bound eta(4) to the W(CO)(3) fragment (cf. [eta(4)-P7W(CO)(3 )](3-)) and eta(1) to the (en)(CO)(3)W fragment via the long W(2)-P(1) bond of 2.643(3) Angstrom. The structure of 4 is similar, with a (C6H 11)(3)Sn+ group attached to the P(1) atom of the [eta(4)-P7W(CO)(3)](3 -) complex. The coordination geometry at P(1) is distinctly pyramidal in both compounds, which leaves the ions with no crystallographic symm etry, For complexes 39 and 3b, two fluxional processes are rapid on th e NMR time scale at -50 degrees C (202 MHz) that give the P-7 cages vi rtual C-2v symmetry in solution and AA'A '' A'''M '' X spin systems. T hese processes are (1) a wagging of the four P atoms bound to the M(CO )(3) units and (2) rapid inversion at P(1). For 4, inversion at phosph orus becomes slow on the NMR time scale at low temperature (-50 degree s C, 83 MHz) with Delta G(double dagger) = 13 kcal/mol. Crystallograph ic data are as follows. [K(2,2,2-crypt)](3)3b en: triclinic, P (1) ove r bar, a = 14.396(4) Angstrom, b = 17.543(3) Angstrom, c = 20.518(2) A ngstrom, alpha = 82.419(11)degrees, beta = 76.830(14)degrees, gamma = 69.16(2)degrees, V = 4708(2) Angstrom(3), Z = 2, R(F) = 5.52%, R-w(F-2 ) = 14.31%. [K(2,2,2-crypt)](2)4: triclinic, P (1) over bar, a = 12,24 7(2) Angstrom, b = 15.1909(14) Angstrom, c = 21.292(3) Angstrom, alpha = 97.374(10)degrees, beta = 93.273(13)degrees, gamma = 111.217(9)degr ees, V = 3639.8(8) Angstrom(3), Z = 2, R(F) 10.50%,R-w(F-2) = 20.21%.