Cationic carbonylmanganese complexes of the olefinic ligand tri(1-cyclohepta-2,4,6-trienyl)phosphane, P(C7H7)3

A series of tetrafluoroborate salts of carbonylmanganese cations was obtained which contain the olefinic phosphane, P(C7H7)3 (1). Whereas 1 is a conventional two-electron phosphane ligand ([P]) in {Mn(CO)5[P]}BF4 (2)—as in the neutral bromide or trifluoroacetate complexes, cis-{Mn(X)(CO)4[P]}BF4 (X=Br (4b), CF3COO (4d)) and mer,trans-{Mn(X)(CO)3[P]}BF4 (X=Br (5b), CF3COO (5d))—it is transformed into a four-electron chelate ligand ([P′]) if 4b and 5b react with AgBF4 to give cis-{Mn(CO)4[P′]}BF4 (7) and mer,trans-{Mn(CO)3[P][P′]}BF4 (8), respectively, ([P′]=P(C7H7)2(η2-C7H7)). An analogous halide abstraction by AgBF4 converts mer-{Mn(I)(CO)3[P′]} (6c) into fac-{Mn(CO)3[P″]}BF4 (9) which contains the phosphane as a six-electron ligand ([P″]) with an η4-norcaradienyl ring ([P″]=P(C7H7)2(η4-C7H7)). The coordinated η2-cyclohepta-2,4,6-trienyl substituent in 7 and 8 is displaced by tert-butyl isocyanide (L) to give cis-{Mn(CO)4[P](L)}BF4 (10) and mer,trans-{Mn(CO)3[P]2(L)}BF4 (11), respectively. The structures of the new cations have been assigned on the basis of their carbonyl stretching absorption patterns in the IR spectra and by their 1H-, 13C- and 31P-NMR spectra. Single-crystal X-ray structure analyses were carried out for 7 and 9.