CARBONYLIRON-LEAD COMPLEXES - MULTINUCLEAR MAGNETIC-RESONANCE STUDY IN SOLUTION AND X-RAY STRUCTURE DETERMINATION OF [ET(2)PBFE(CO)(4)](2)

Complexes of the types R(3)Pb-Fe(CO)(2)Cp [R = Me (1a), Et (1b), Pr-l (1c), (t)Bu (1d)], R(2)Pb[Fe(CO)(2)Cp](2) [R = Me (2a), Et (2b)], Pr-l(2)(Br)Pb-Fe(CO)(2)Cp (3c) and [R(2)PbFe(CO)(4)](2) [R = Me (4a), Et (4b), Pr-l (4c)], as well as the spiro-complexes Pb[Fe(CO)(4)PbR(2)](2) [R = Me (5a), Et (5b), Pr-l (5c)] and Pb[Fe(CO)(4)](4) (6) were studied by multinuclear magnetic resonance spectroscopy (H-1, C-13, Pb-207 NMR). For the first time, coupling constants (1)J((PbFe)-Pb-207-Fe-57) were determined, covering a range between 33.5 (6) and 117 Hz (4a). The magnitude of the geminal coupling constants \2J((PbPb)-Pb-207-Pb-207)\ in the spiro-compounds 5 decreases from 1090.0 Hz (5a) to 377.0 Hz (5c). The signs of the coupling constants (n)J((PbC(R)-Pb-207-C-13)) (n = 1, 2) and (n)J((PbH(R)-Pb-207-H-1)) (n = 2, 3) were determined by various 2D NMR experiments. Among all known Pb(IV) compounds the lowest Pb-207 nuclear magnetic shielding was found in Pb[Fe(CO)(4)](4) (6): delta(207)Pb +3586.6. According to the single crystal X-ray structure determination of 4b (orthorhombic; space group Pbca; a = 967.4, b = 1367.7, c = 1772.4 pm), the Pb2Fe2 ring is planar with bond angles FePbFe = 102.8 degrees and PbFePb = 77.2 degrees, and there is a relatively short transannular distance of 340.8 pm between the two lead atoms.