OCCURRENCE OF A MU-SIF INTERACTION IN BIMETALLIC TRIFLUOROSILYL COMPLEXES

With the aim of inducing a mu-SiF interaction between two metal centres, MeO was replaced by F on the silicon atom involved in mu-SiO bonding with a bimetallic unit by the reaction of mer-[(OC)3 activated Fe{mu-Si(OMe)2(OMe)}(mu-dppm)PdCl)] 1 (dppm = Ph2PCH2PPh2) with BF3. However, the desired complex mer-[(OC)3 activated Fe{mu-SiF2(F)}(mu-dppm)PdCl] 3 could only be characterised in solution. From the solution structure of the reaction intermediate mer-[(OC)3 activated Fe{mu-SiF2(OMe)}(mu-dppm)PdCl] 2 where a MeO --> Pd interaction in preference to F --> Pd is suggested on the basis of spectroscopic data, it appears that the dative F --> Pd interaction is weaker than the corresponding MeO --> Pd one. In the presence of an excess of BF3, rupture of the Fe-Si bond of 3 eventually occurred in CH2Cl2, resulting in the formation of [(OC)3 activated Fe(mu-Cl)(mu-dppm)PdCl] 4a. When the complex mer-[{(MeO)3Si}(OC)3 activated Fe(mu-dppm)PtH(PPh3)] 5 was treated with BF3.Et2O, the trifluorosilyl derivative mer-[(F3Si)(OC)3 activated Fe(mu-dppm)PtH(PPh3)] 6 was obtained and isolated in 87% yield. The structure of its benzene solvate 6.0.5C6H6 was determined by X-ray diffraction: triclinic, space group P1BAR, a = 17.692(7), b = 13.084(5), c = 11.031(5) angstrom, alpha = 112.16(1), beta = 91.31(2), gamma = 101.71(1)-degrees and Z = 2. It has been solved by Patterson and Fourier methods and refined by full-matrix least squares to R = 0.0408 for 5870 observed reflections. The Fe and Pt atoms are at a distance of 2.661(1) angstrom, consistent with a metal-metal bond. The nearly square-planar co-ordination of Pt involves also one P atom from dppm, one PPh3 and a hydride. The co-ordination of Fe is completed by three carbonyl groups, a P atom of the dppm ligand, and the SiF3 ligand. Noteworthy are the weak intramolecular interactions between the hydride and two F atoms from the SiF3 ligand [H...F2.39(7) and 2.50(6) angstrom]. The IR and NMR (H-1, P-31-{H-1} and F-19-{H-1}) spectra of the new complexes are reported and discussed.