The complex [Rh(CO)Cl{Me 2 PC(Me)=C(Me)BMe 2 } 2 ] (5) has been prepared again in order to prove its structure with weak bonding interactions between the basic rhodium centre and the Lewisacidic Me 2 B group of the donor/acceptor ligand Me 2 PC(Me)=C(Me)BMe 2 (1). For further investigations additional ligands with P-donor and B-acceptor centres, e. g. Ph 2 PC(Ph)=C(Ph)BPh 2 (2), B(OCH 2 PMe 2 ) 3 (3), and B(CH 2 CH 2 PMe 2 ) 3 (4), have been prepared and the coordinating properties have been studied by reactions of 1 and 4 with [(π-C 5 Me 5 )Rh(CO) 2 ] and Pd(PPh 3 ) 4 , respectively. Because single crystals of the products [(π-C 5 Me 5 )Rh(CO)Me 2 PC(Me)=C(Me)BMe 2 ] (6), [(π-C 5 Me 5 )Rh(CO){Me 2 PC(Me)=C(Me)BMe 2 } 2 ] (7) as well as [Pd{B(CH 2 CH 2 PMe 2 ) 3 }] (8) or [(Ph 3 P)Pd{B(CH 2 CH 2 PMe 2 ) 3 }] (9) could not be generated, quantum chemical calculations have been used to elucidate the coordination geometry expected for 5, 8 and 9. The calculations support the structure of 5 within the expected limitations of the experimental and theoretical methods andin spite of the extremely soft coordination sphere of 8 and 9 -are in accord with spectroscopic results for the cage structures.

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The tripod phosphane ligand FSi(CH2CH2PMe2)3 (1) has been prepared again and attempts to generate F3CSi(CH2CH2PMe2)3 (2) were undertaken for the preparation of transition metal cage compounds of the type A(CCP)3M or A(CCP)3M-L (A = FSi, F3CSi). The photochemical addition of dimethylphosphane to trifluoromethyl-trivinylsilane, however, gave 1 instead of the expected CF3Sitripod ligand 2, obviously due to difluorocarbene elimination. 1 was used to prepare the chromium carbonyl derivative (CO)3Cr[(Me2PCH2CH2)3SiF] (3) from Cr(CO)3CHT, and 3 was characterized by NMR and IR spectroscopy. The novel complex FSi(CH2CH2PMe2)3Pd (4) and its PPh3 derivative [FSi(CH2CH2PMe2)3Pd]PPh3 (5) have been obtained by reacting 1 with Pd(PPh3)4 and were characterized by NMR (4) and X-ray diffraction (5). The data prove the expected Pd→Si interaction by characteristic coordination shifts and a Pd-Si distance of 3.875 Å which is smaller than the Ni-Si distance in the corresponding nickel compound (3.92 Å ). The preparation of the analogous platinum complex from the precursors Pt(PPh3)4, Pt(C7H10)3, or (Ph3P)2Pt(η2-C2H4) failed, whereas the reaction of 1 with Pt(PEt3)4 was successful, but surprisingly led to the trinuclear complex [FSi(CH2CH2PMe2)3Pt]3(PMe2CH2CH2)3SiF (6) with three cages of type 4 and an additional ligand 1 as a bridging unit. Complex 6 was isolated and characterized spectroscopically. Quantum chemical calculations have been used to elucidate the coordination geometry expected for 4, 5 and the corresponding platinum cage 4′ in 6. The calculations support the structure of 5 within the expected limitations of the experimental and theoretical methods and - in spite of the extremely soft coordination sphere of the studied cages - are in accord with the spectroscopic results.

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