Synthesis and Reactions of a Cyclopentadienyl-Amidinate Titanium tert-Butoxyimido Compound

Journal article

We report the first detailed reactivity study of a group 4 alkoxyimido complex, namely CpTi{PhC(NiPr)2}(NOtBu) (19), with heterocumulenes, aldehydes, ketones, organic nitriles, ArF5CCH, and B(ArF5)3 (ArF5 = C6F 5). Compound 19 was synthesized via imide/alkoxyamine exchange from CpTi{PhC(NiPr)2}(NtBu) and tBuONH2. Reaction of 19 with CS2 and Ar′NCO (Ar′ = 2,6-C6H3iPr 2) gave the [2 + 2] cycloaddition products CpTi{PhC(N iPr)2}{SC(S)N(OtBu)} and CpTi{PhC(N iPr)2}{N(OtBu)C(NAr′)O}, respectively, whereas reaction with 2 equiv of TolNCO afforded CpTi{PhC(NiPr) 2}{OC(NTol)N(Tol)C(NOtBu)O} following a sequence of cycloaddition-extrusion and cycloaddition-insertion steps. Net NOtBu group transfer was observed with both tBuNCO and PhC(O)R, yielding the oxo-bridged dimer [CpTi{PhC(NiPr)2}(μ-O)] 2 and either the alkoxycarbodiimide tBuNCNOtBu or the oxime ethers PhC(NOtBu)R (R = H (25a), Me (25b), Ph (25c)). DFT studies showed that in the reaction with PhC(O)R (R = H, Me) the product distribution between the syn and anti isomers of PhC(NOtBu)R was under kinetic control. Reaction of 19 with ArCN gave the Ti=Nα insertion products CpTi{PhC(NiPr)2}{NC(Ar)NO tBu} (Ar = Ph (28), 2,6-C6H3F2 (27), ArF5 (26)) containing tert-butoxybenzimidamide ligands. Reaction of 19 or 26 with an excess of ArF5CN gave CpTi{PhC(NiPr) 2}{NC(ArF5)NC(ArF5)N(C{ArF5}NO tBu)} (29) following net head-to-tail coupling of 2 equiv of ArF 5CN across the Ti=Nα bond of 26. Reductive N α-Oβ bond cleavage was observed with ArF 5CCH, forming CpTi(OtBu){NC(ArF5)C(H)N( iPr)C(Ph)N(iPr)} (30). Addition of 2 equiv of [Et 3NH][BPh4] to 19 in THF-d8 resulted in protonolysis of the amidinate ligand, forming [PhC(NHiPr) 2][BPh4] and the cationic alkoxyimido complex [CpTi(NOtBu)(THF-d8)2]+. In contrast, reaction with B(ArF5)3 resulted in elimination of isobutene and formation of CpTi{PhC(NiPr)2} {η2-ON(H)B(ArF5)3}. © 2013 American Chemical Society.

Authors: Groom, L; Schwarz, A; Nova, A; Clot, E; Mountford, P

• Publication status: Published
• Publisher: American Chemical Society
• Journal: ORGANOMETALLICS
• Volume: 32
• Issue: 24
• Pages: 7520-7539
• Publication date: 2013-12-23
• DOI: 10.1021/om401008a
• EISSN: 1520-6041
• ISSN: 0276-7333
• Language: English