ALTERNATIVE LIGANDS .31. NICKELCARBONYL C OMPLEXES OF TRIPOD LIGANDS OF THE TYPE XM'(OCH2PME2)N(CH2CH2PR2)3-N (M'=SI, GE - N=0-3)

The coordinating properties of the tripod ligands RM'(OCH2PMe2)n(CH2CH 2PMe2)3-n (M' = Si, Ge) (1-7), MeSi(OCH2PMe2)2CH2CH2P(CF3)2 (8), MeSi( OCH2PMe2)2CH2CH2NMe2 (10) as well as of the tetradentate representativ e Si(OCH2PMe2)4 (9) have been investigated by the preparation of the n ovel nickel carbonyl complexes LNiCO (11-18), Si(OCH2PMe2)4[Ni(CO)2]2 (19) and (HOCH2PMe2)2Ni(CO)2 (20). They are obtained in moderate to go od yields by the reaction of Ni(CO)4 with the corresponding ligands in toluene (20 - 111-degrees-C) (see Table 1). The new compounds have be en characterized by analytical (C, H) and spectroscopic investigations (IR; H-1-, C-13-, F-19-, P-31-NMR, MS). The ligand properties are dis cussed on the basis of spectroscopic data [in particular coordination shifts DELTAdelta = delta(complex)-delta(ligand)] leading to the concl usion that the high electron density on Ni gives rise to a weak, but s ignificant Ni --> Si interaction. An important indication comes from t he large low field shift DELTAdelta(F) = 34.5 ppm for the SiF acceptor bridge in 17. This result is supported by an X-ray diffraction study of 11 giving an NiSi distance of 3.941(2) angstrom. With the exception of O2 . . . P3 (Abb. 7) all other O. . . P through-cage contacts are longer than the NiSi distance. An additional release from the high cha rge density on Ni is obtained via pi-backbonding to the neighbouring g roups OCPMe2, CCPMe2 and CO.