CHEMISTRY OF C-TRIMETHYLSILYL-SUBSTITUTED HETEROCARBORANES .21. SYNTHESES, STRUCTURES, EPR-SPECTRA, AND REACTIVITIES OF BENT-SANDWICH AND HALF-SANDWICH TITANACARBORANES - FULL ANALYSIS OF SPIN-SPIN COUPLING IN2 STRUCTURALLY CHARACTERIZED TITANIUM(III)-CARBORANE DIMERS
Ns. Hosmane et al., CHEMISTRY OF C-TRIMETHYLSILYL-SUBSTITUTED HETEROCARBORANES .21. SYNTHESES, STRUCTURES, EPR-SPECTRA, AND REACTIVITIES OF BENT-SANDWICH AND HALF-SANDWICH TITANACARBORANES - FULL ANALYSIS OF SPIN-SPIN COUPLING IN2 STRUCTURALLY CHARACTERIZED TITANIUM(III)-CARBORANE DIMERS, Organometallics, 16(7), 1997, pp. 1365-1377
The reaction of Cp(2)TiCl(2) with the unsolvated dilithium compounds c
loso-exo-Li-1-Li-2-(R)-3-(SiMe(3))-2,3-C2B4H4 (R = SiMe(3), Me, H) pro
duced dimeric mixed-ligand sandwich titanacarboranes mo-1-Cp-1-Ti(III)
-2-(R)-3-(SiMe(3))-2,3-C2B4H4](2) (R = SiMe(3) (1), Me (2), H (3)) in
yields of 60%, 54%, and 60%, respectively. The chemical oxidation of t
hese titanacarboranes in the presence of TiCl4 in THF resulted in the
formation of the corresponding diamagnetic Ti(IV) species -1-(CI)-1-(T
HF)-1-Ti-2-(R)-3-(SiMe(3))-2,3-C2B4H4) (R = SiMe(3) (7), Me (8), H (9)
) in 86%, 58%, and 45% yields, respectively. When the bis(trimethylsil
yl)-substituted dilithiacarborane precursor was reacted with TiCl3, on
ly the monomeric full-sandwich chlorotitanacarborane (2)[1-Cl-1,1'-Ti-
(2,3-(SiMe(3))(2)-2,3-C2B4H4)(2)] (4) was produced, while replacement
of a SiMe(3) group with a less sterically demanding Me group afforded
the dimeric titanacarborane DA)](2)[1,1'-Ti-(2-Me-3-SiMe(3)-2,3-C2B4H4
)(2)](2) (5A). On the other hand, when the TMEDA-solvated i(TMEDA)]-1-
Li[(TMEDA)-2,4-(SiMe(3))(2)-2,4-C2B4H4 was the precursor, reaction wit
h TiCl3 yielded only the corresponding monomeric half-sandwich chlorot
itanacarborane (TMEDA)-1-Cl-1-Ti(III)-2,4-(SiMe(3))(2)-2,4-C2B4H4 (6)
In addition to the X-ray analyses of 1, 5A, 6, and 7, the Ti(III) comp
ounds and an electrochemically generated Ti(TV)/Ti(III) mixed-valence
complex (5B) were characterized by EPR spectroscopy. The dimers 1 and
5A exhibit unusually well-resolved triplet EPR features, which were fu
lly analyzed and correlated with the structural results. Magnetic susc
eptibility measurements reveal a rather; small d(1)-d(1) exchange coup
ling constant of -45.8 cm(-1) (antiferromagnetic interaction) for 1. T
he one-electron oxidation of 5A produced an anion (S = 1/2) with rhomb
ic EPR features, which was tentatively identified as a delocalized [Ti
(+3.5)](2) mixed-valence species (5B).