Rapid Inversion at Phosphorus in the [η4-(C6H11)3SnP7W(CO)3]2- and [(en)(CO)3W(η1,η4-P7)M(CO)3]3- Ions Where M = Cr, W

Ethylenediamine (en) solutions of [η4-P7M(CO)3]3- ions [M = Cr (1a), W (1b)] react with (mesitylene)W(CO)3 to form the bimetallic complexes [(en)(CO)3W(η1,η4-P7)M(CO)3]3- where M = Cr (3a), W (3b) in good yield. Compound 3b can be prepared directly from P7 3- and 2 equiv of (mesitylene)W(CO)3. Compound 3a reacts with 1 equiv of P7 3- to form 1a and 1b. En solutions of 1b react with 1 equiv of (C6H11)3SnCl to give [η4-(C6H11)3SnP7W(CO)3]2- (4) in good crystalline yield as the [K(2,2,2-crypt)]+ salt. The X-ray structure of the [K(2,2,2-crypt)]+ salt 3b revealed a norbornadiene-like P7 cage bound η4 to the W(CO)3 fragment (cf. [η4-P7W(CO)3]3-) and η1 to the (en)(CO)3W fragment via the long W(2)−P(1) bond of 2.643(3) Å. The structure of 4 is similar, with a (C6H11)3Sn+ group attached to the P(1) atom of the [η4-P7W(CO)3]3- complex. The coordination geometry at P(1) is distinctly pyramidal in both compounds, which leaves the ions with no crystallographic symmetry. For complexes 3a and 3b, two fluxional processes are rapid on the NMR time scale at −50 °C (202 MHz) that give the P7 cages virtual C 2 v symmetry in solution and AA‘A‘‘A‘‘‘MM‘‘X spin systems. These 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 phosphorus becomes slow on the NMR time scale at low temperature (−50 °C, 83 MHz) with ΔG⧧ = 13 kcal/mol. Crystallographic data are as follows. [K(2,2,2-crypt)]3 3b·en: triclinic, P1̄, a = 14.396(4) Å, b = 17.543(3) Å, c = 20.518(2) Å, α = 82.419(11)°, β = 76.830(14)°, γ = 69.16(2)°, V = 4708(2) Å3, Z = 2, R(F) = 5.52%, R w(F 2) = 14.31%. [K(2,2,2-crypt)]2 4: triclinic, P1̄, a = 12.247(2) Å, b = 15.1909(14) Å, c = 21.292(3) Å, α = 97.374(10)°, β = 93.273(13)°, γ = 111.217(9)°, V = 3639.8(8) Å3, Z = 2, R(F) = 10.50%, R w(F 2) = 20.21%.