Five-Coordinate Carbides in Ti-Al-C Complexes

Abstract

Triple C−H bond activation in the reaction of [Cp(R3PN)Ti(Me)2] with AlMe3 affords Ti‐Al‐C aggregates. These species 1 and 2 exist in equilibrium with AlMe3, thus demonstrating a highly facile interconversion of carbide species with distorted tetrahedral and five‐coordinate, pseudo‐trigonal‐bipyramidal geometries, respectively. R=iPr.

Reactions of the titanium-carbide species CpTi(μ2-Me)(μ2-NPi-Pr3)(μ4-C)(AlMe2)3

“…The Ti-carbide species CpTi(l 2 -Me)(l 2 -NPi-Pr 3 )-(l 4 -C)(AlMe 2 ) 3 was prepared as was previously described [26,27], and we have now explored reactions of this species with a variety of reagents. Few of these efforts yielded new products, and in no case was there evidence of reaction at the carbide carbon.…”

“…that lead to multiple C-H activation processes. For example, reactions of CpM(NPR 3 )Me 2 (M = Ti, Zr) with excess AlMe 3 , result in the formation of the Ti-carbide species CpTi(l 2 -Me)(l 2 -NPR 3 )(l 4 -C)(AlMe 2 ) 3 (a), or CpTi(l 2 -Me)(l 2 -NPR 3 )(l 5 -C)(AlMe 2 ) 3 AE (AlMe 3 ) [26,27] (b) and the Zr-methanide derivatives, (Cp * Zr) 4 -(l-Cl) 5 (Cl)(l-CH) 2 and (Cp * Zr) 5 (l-Cl) 6 (l-CH) 3 [28]. Additionally, we have published the mechanistic details of the divergent C-H activation pathways observed in the reaction of (t-Bu 3 PN) 2 TiMe 2 with AlMe 3 , which affords [(l 2 -tBu 3 PN)Ti(l-Me)(l 4 -C)(AlMe 2 ) 2 ] 2 (c) and (t-Bu 3 PN)Ti-(l 2 -t-Bu 3 PN)(l 3 -CH 2 ) 2 (AlMe 2 ) 2 (AlMe 3 ) (d) [29].…”

“…The Ti-C distance to the carbide carbon is 1.851(12) Å and is shorter than that reported for CpTi(l 2 -Me)(l 2 -NPi-Pr 3 )(l 4 -C)(AlMe 2 ) 3 (1.891(6) Å ) and CpTi(l 2 -Me)(l 2 -NPR 3 )(l 5 -C)(AlMe 2 ) 3 AE (AlMe 3 ) (1.878(4) Å ) [26,27]. In contrast, the carbide-C-Al distances in 1 are slightly longer (1.990(12) Å , 2.009(12) Å , 1.985(11) Å ) compared to those in than those in CpTi(l 2 -Me)(l 2 -NPiPr 3 )(l 4 -C)(AlMe 2 ) 3 (1.974(6) Å ) [26,27]. This presumably reflects donation of electron density from the chlorides to the Al atoms which increases the relative acidity of the Ti center, thus shortening the Ti-C bond.…”

“…Combustion analyses were done in house employing a Perkin Elmer CHN Analyzer. CpTi(l 2 -Me)(l 2 -NPi-Pr 3 )(l 4 -C)(AlMe 2 ) 3 was prepared as previously described [26,27]. ClSnMe 3 (0.038 g; 0.194 mmol) was added to a solution of CpTi(l 2 -Me)(l 2 -NPi-Pr 3 )(l 4 -C)(AlMe 2 ) 3 (0.047 g; 0.097 mmol) in C 6 H 6 .…”

“…Our interest in C-H bond activation lies in the potential to generate unusual transition metal derivatives. In our own work we have recently described the reactions of Ti and Zr-phosphinimide complexes with the Lewis acid AlMe 3 [26,27]. that lead to multiple C-H activation processes.…”