Formation of Intramolecular Rings in Ferramonocarbollide Complexes

Addition of PPh2Cl and Tl[PF6] to CH2Cl2 solutions of [N(PPh3)2][6,6,6-(CO)3-closo-6,1-FeCB8H9] (1) affords the isomeric B-substituted species [6,6,6-(CO)3-n-(PHPh2)-closo-6,1-FeCB8H8] [n = 7 (2a) or 10 (2b)]. Deprotonation (NaH) of the phosphine ligand in 2a, with subsequent addition of [IrCl(CO)(PPh3)2] and Tl[PF6], yields the neutral, zwitterionic complex [6,6,6-(CO)3-4,7-μ-{Ir(H)(CO)(PPh3)2PPh2}-closo-6,1-FeCB8H7] (3), which contains a B−P−Ir−B ring. Alternatively, deprotonation using NEt3, followed by addition of HCCCH2Br, affords [6,6,6-(CO)3-7-(PPh2CCMe)-closo-6,1-FeCB8H8] (4). Addition of [Co2(CO)8] to CH2Cl2 solutions of the latter gives [6,6,6-(CO)3-7-(PPh2-{(μ-η2:η2-CCMe)Co2(CO)6})-closo-6,1-FeCB8H8] (5), which contains a {C2Co2} tetrahedron. In the absence of added substrates, deprotonation of the PHPh2 group in compounds 2, followed by reaction of the resulting anions with CH2Cl2 solvent, affords [6,6,6-(CO)3-n-(PPh2CH2Cl)-closo-6,1-FeCB8H8] [n = 7 (6a) or 10 (6b)] plus [6,6-(CO)2-6,7-μ-{PPh2CH2PPh2}-closo-6,1-FeCB8H8] (7, formed from 2a), of which the latter species possesses an intramolecular B−P−C−P−Fe ring. Addition of Me3NO to CH2Cl2 solutions of 2a causes loss of an Fe-bound CO ligand and formation of [6,6-(CO)2-6,7-μ-{NMe2CH2PPh2}-closo-6,1-FeCB8H8] (8), which incorporates a B−P−C−N−Fe ring. A similar reaction in the presence of ligands L yields [6,6-(CO)2-6-L-7-(PPh2CH2Cl)-closo-6,1-FeCB8H8] [L = PEt3 (9) or CNBut (10)], in addition to 8.