Chemistry of C-trimethylsilyl-substituted heterocarboranes. 9. Reactivity of closo-germa- and closo-plumbacarboranes toward a monodentate Lewis base, (ferrocenylmethyl)dimethylamine: synthetic, structural, and bonding studies on the donor-acceptor complexes 1-M[(.eta.5-C5H5)Fe(.eta.5-C5H4CH2(Me)2N)]-2-(SiMe3)-3-R-2,3-C2B4H4 (M = Ge, Pb; R = SiMe3, Me, H)

Abstract

cioso-l-Ge-2-(Si(CH3)3)-3-R-2,3-C2B4H4 (R = Si(CH3)3 (I), CH3 (II), and H (III)) and c/oso-l-Pb-2-(Si(CHs)3)-3-R-2,3-C2B4H4 (R = Si(CH3)3 (VII), CH3 (VIII), and H (IX)) react with (ferrocenylmethyl)dimethylamine (ferrocene amine) in dry benzene to give the corresponding donor-acceptor adducts IV-VI and X-XII, respectively, in yields ranging from 56% to 79%. Complex X was converted into two crystal modifications, X(A) and X(B), by slow crystal growth from ferrocene amine and by slow sublimation in vacuo, respectively. The crystal structures of IV, X(A), and X(B) were determined by single-crystal X-ray diffraction. All show that the nitrogen of the ferrocene amine base bonds to the capping metal of the metallacarborane. The metal is not symmetrically bonded to the atoms of the C2B3 face but is slipped toward the boron side of the face, giving a distorted-pentagonal-bipyramidal MC2B4 cage. Similarities in the NMR and IR spectra of IV-VI and X-XII indicate that all complexes have similar structures. The unit cells of both IV and X(B) contain two crystallographically independent molecules; in one the metal-base nitrogen bond is in the mirror plane of the MC2B4 cage, while in the other the bond is slightly rotated out of this plane. The molecules in the unit cell of X(A) are identical. In all structures the ferrocenyl groups are rotated toward the metallacarboranes so that some of the metal-ferrocene distances are within their van der Waals radii. Fenske-Hall molecular orbital calculations show that there are direct interactions between the metal and the Cp(z-) orbitals of the ferrocenyl group. It is suggested that the stability gained by such interactions is responsible for the non sterically favorable positions of the ferrocenes. Complexes IV, X(A), and X(B) all crystallized in the triclinic space group PI with a = 12.633 (3), 10.106 (3), and 12.677

1-(N,N-Dimethylferrocenylmethylamine)-2-methyl-3-(trimethylsilyl)-2,3-dicarba-1-plumba-closo-heptaborane(6)

“…It has been speculated that an extended CzB4-Sn-Cp-Fe-Cp interaction might contribute to this anomalous chemical shift behavior (Hosmane, Fagner, Zhu, Siriwardane, Maguire, Zhang & Pinkston, 1989). To our surprise, the same structural features were found for the corresponding Ge and Pb analo- Hosmane, Lu, Zhang, Maguire, Jia & Barreto, 1992]. Noting that both (1) and (2) carry a bulky SiMe3 group on each cage C atom, the question arose whether the presence of a less bulky group such as Me on one of the cage C atoms would also yield the same configuration of the Lewis base, N,N-dimethylferrocenylmethylamine, in the complex such that it is in a position of maximum steric interaction.…”

“…2). Thus, the present work establishes the existence of the secondary metal-CsH5 (70 interactions in this type of adduct for complex stabilization and furthermore it provides a general structural pattern for these systems (Hosmane, Fagner, Zhu, Siriwardane, Maguire, Zhang & Pinkston, 1989;Hosmane, Lu, Zhang, Maguire, Jia & Barreto, 1992). …”

“…, in which one of the cage C atoms carries a methyl group, was synthesized as described by Hosmane, Lu, Zhang, Maguire, Jia & Barreto (1992) and its crystals were grown very slowly from a solution containing 95% anhydrous N,N-dimethylferrocenylmethylamine and 5% dry benzene. We report herein the results of the subsequent structural investigation.…”

Recent Advances in the Chemistry of Heterocarborane Complexes Incorporating s- and p-Block Elements

“…On the contrary, their chemistry is dominated by Lewis acid behavior. All of the half-sandwich metallacarboranes of germanium, tin, and lead have been found to form donor−acceptor complexes with monodentate, ,− bidentate, ,,,,− bis(bidentate) , , and tridentate , bases. The bonding in these complexes have been the subject of several theoretical studies. ,, Figure shows the structure of the 1-(2,2‘-C 10 H 8 N 2 )-2,3-(SiMe 3 ) 2 -1,2,3-SnC 2 B 4 H 4 complex; Figure , the 1-(2,2‘:6‘,2‘‘-C 15 H 11 N 3 )-2,3-(SiMe 3 ) 2 -1,2,3-SnC 2 B 4 H 4 ; and Figure , that of 1-(THF)-2,3-(Me) 2 -1,2,3-SnC 2 B 9 H 9 …”

“…In this complex, it is an open question whether the base would be better described as functioning as a bidentate rather than a tridentate ligand. The complexes formed by the group 14 metallacarboranes with monodentate bases are shown in Figures , , and 44. ,, As with their polydentate analogues, the bases reside over the boron side of the C 2 B 3 bonding face of the carborane and the metals are slip distorted in the direction of base orientation. The same explanations used in rationalizing these distortions in the bidentate bases are operable in monodentate base complexes.…”