Structures and stabilities of adducts of carbenes and fullerenes, C60(CR2)n, R = H, CH3, C4H9 and n=1-6

The addition of carbenes to C-60 to form C-60(CR2)(n) where R = H, CH3, tert-C4H9 and n = 1-6 has been investigated using the AM1 Hamiltonian and the program MOPAC 6.0. Addition to a carbon-carbon bond can be at a polyhedral edge shared between a C-5 and a C-6 ring, the pent-hex edge, or to an edge shared between two C-6 rings, the hex-hex edge. In each case the edge carbon-carbon bond can remain intact or be broken. Different behaviour is observed for the addition of CH2, C(CH3)(2) and C(C4H9)(2). The most important types of addition lead to the formation of pent-hex bond broken isomers and hex-hex bond intact isomers. The hex-hex bond broken isomer, however, exists as a local energy minimum for C-60(CH2)(n), n = 1, 2, 3 and C-60[C(CH3)(2)](n,) n = 2, 3, and the pent-hex bond intact isomer is a local energy minimum for C-60[C(C4H9)(2)]. Successive addition of CH2 groups results in a clustering together of these groups with an opening out of a hole in the structure. Addition of successive C(CH3)(2) groups or C(C4H9)(2) groups leads to structures in which these groups are well separated from each other and may be on pent-hex or hex-hex edges for C(CH3)(2), or hex-hex edges for C(C4H9)(2). (C) 2001 Elsevier Science B.V. All rights reserved.