Formation of Intramolecular Rings in Ferramonocarbollide Complexes

Addition of PPh 2 Cl and Tl[PF 6 ] to CH 2 Cl 2 solutions of [N(PPh3)2][6,6,6-(CO)3-closo-6,1-FeCB 8 H 9 ] (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 [lrCl(CO)(PPh 3 ) 2 ] and Tl[PF 6 ], yields the neutral, zwitterionic complex [6,6,6-(CO) 3 -4,7-μ-{lr(H)(CO)(PPh 3 ) 2 PPh 2 }-closo-6,1-FeCB 8 H 7 ] (3), which contains a B-P-lr-B ring. Alternatively, deprotonation using NEt 3 , followed by addition of HC≡CCH 2 Br, affords [6,6,6-(CO) 3 -7-(PPh 2 C≡CMe)-closo-6,1-FeCB 8 H 8 ] (4). Addition of [Co 2 (CO) 8 ] to CH 2 Cl 2 solutions of the latter gives [6,6,6-(CO) 3 -7-(PPh2-{(μ-η 2 :η 2 -C≡CMe)Co2(CO)6})-closo-6,1-FeCB8H8] (5), which contains a {C 2 Co 2 } tetrahedron. In the absence of added substrates, deprotonation of the PHPh 2 group in compounds 2, followed by reaction of the resulting anions with CH 2 Cl 2 solvent, affords [6,6,6-(CO) 3 -n-(PPh2CH2CI)-closo-6,1-FeCB 8 H 8 ] [n = 7 (6a) or 10 (6b)] plus [6,6-(CO)2-6,7-μ-{PPh 2 CH 2 PPh 2 }-closo-6,1-FeCB 8 H 8 ] (7, formed from 2a), of which the latter species possesses an intramolecular B-P-C-P-Fe ring. Addition of Me 3 NO to CH 2 Cl 2 solutions of 2a causes loss of an Fe-bound CO ligand and formation of [6,6-(CO)2-6,7-μ-{NMe 2 CH 2 PPh 2 }-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-(PPh2CH2CI)-closo-6,1-FeCB 8 H 8 ] [L = PEt 3 (9) or CNBU t (10)], in addition to 8.