The effect of a paramagnetic metal ion within a molecule: comparison of the structurally identical paramagnetic [3,3-Fe(1,2-C2B9H11)2]- with the diamagnetic [3,3-Co(1,2-C2B9H11)2]- sandwich complexes.

Abstract

Derivatives of the ferrabisdicarbollide [3,3'-Fe(1,2-C(2)B(9)H(11))(2)](-) have been produced starting from the zwitterion [3,3'-Fe(8-(OCH(2)CH(2))(2)-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))], 1, upon reaction with nucleophiles: alkoxides, halides and hydrosulfide ions HS(-). The result has been the preparation of [3,3'-Fe(8-(OCH(2)CH(2))(2)R/X-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))] (R = OMe, [2](-); OEt, [3](-); OCH(2)CH(2)OCH(3), [4](-); and X = Cl, [5](-); Br, [6](-); I, [7](-); and SH, [8](-)). The reaction behavior of is comparable to the well-studied cobalt equivalent, [3,3'-Co(8-(OCH(2)CH(2))2-1,2-C(2)B(9)H(10))(1',2'-C(2)B(9)H(11))], and the yields and stability of the resulting complexes are similar. These results are relevant taking into account that [3,3'-Fe(1,2-C(2)B(9)H(11))(2))(-) is a paramagnetic anion. Implications of this are observed in the (11)B-, (1)H and (13)C NMR spectra of [3,3'-Co(1,2-C(2)B(9)H(11))(2)](-) and [3,3'-Fe(1,2-C(2)B(9)H(11))(2)](-) that having identical sandwich molecular structures and the same negative charge have absolutely different widths of the NMR field, between 15 and -25 ppm for [3,3'-Co(1,2-C(2)B(9)H(11))(2)](-) and in the range 150 to -550 ppm for [3,3'-Fe(1,2-C(2)B(9)H(11))(2)](-). The sharpness of both spectra is on the other hand comparable, although no B-H couplings are observed in the Fe metallacarborane or its derivatives. Remarkable is the comparative influence vs. [3,3'-Co(1,2-C(2)B(9)H(11))(2)](-) of replacing Co by Fe on the elements of the cluster layer nearest to the metal. The two equivalent C cluster (Cc) atoms are influenced at 36 840 Hz, the two equivalent B atoms that are adjacent to the two Cc are influenced at 38 157 Hz and the single B that is adjacent to the two B atoms is influenced at 44 062 Hz. Remarkable is the similar influence on B and on C, taking into account that the values have been obtained from two distinct NMR spectra of (11)B and (13)C. The {(11)B-(11)B} COSY NMR and {(1)H-(11)B} HETEROCOSY NMR spectra of [3,3'-Fe(1,2-C(2)B(9)H(11)(2)](-) have been obtained and are reported for the first time.