title: Rapid Inversion at Phosphorus in the [eta(4)-(C(6)H(11))(3)SnP(7)W(CO)(3)](2)(-) and [(en)(CO)(3)W(eta(1),eta(4)-P(7))M(CO)(3)](3)(-) Ions Where M = Cr, W.
abstract: Ethylenediamine (en) solutions of [eta(4)-P(7)M(CO)(3)](3)(-) ions [M = Cr (1a), W (1b)] 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 (3a), 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 equiv of P(7)(3)(-) to form 1a and 1b. En solutions of 1b react with 1 equiv of (C(6)H(11))(3)SnCl to give [eta(4)-(C(6)H(11))(3)SnP(7)W(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 P(7) cage bound eta(4) to the W(CO)(3) fragment (cf. [eta(4)-P(7)W(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) Å. The structure of 4 is similar, with a (C(6)H(11))(3)Sn(+) group attached to the P(1) atom of the [eta(4)-P(7)W(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 degrees C (202 MHz) that give the P(7) 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 degrees C, 83 MHz) with DeltaG() = 13 kcal/mol. Crystallographic data are as follows. [K(2,2,2-crypt)](3)3b.en: triclinic, P&onemacr;, a = 14.396(4) Å, b = 17.543(3) Å, c = 20.518(2) Å, alpha = 82.419(11) degrees, beta = 76.830(14) degrees, gamma = 69.16(2) degrees, V = 4708(2) Å(3), Z = 2, R(F) = 5.52%, R(w)(F(2)) = 14.31%. [K(2,2,2-crypt)](2)4: triclinic, P&onemacr;, a = 12.247(2) Å, b = 15.1909(14) Å, c = 21.292(3) Å, alpha = 97.374(10) degrees, beta = 93.273(13) degrees, gamma = 111.217(9) degrees, V = 3639.8(8) Å(3), Z = 2, R(F) = 10.50%, R(w)(F(2)) = 20.21%.
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742.
authors.forename: Scott
authors.initials: S
authors.lastname: Charles
authors.forename: Janet A.
authors.initials: JA
authors.lastname: Danis
authors.forename: James C.
authors.initials: JC
authors.lastname: Fettinger
authors.forename: Bryan W.
authors.initials: BW
authors.lastname: Eichhorn