Reactions of Cyclopentadienyl-Amidinate Titanium Imido Compounds with CS2, COS, Isocyanates, and Other Unsaturated Organic Compounds

Abstract

New single-, double-, and cross-coupling and imido group transfer reactions of cyclopentadienyl-amidinate titanium imido complexes are described. Reaction of Ti(η-C5R4Me)(NtBu)Cl(py) (R = Me or H) with the lithiated benzamidinate Li[PhC(NSiMe3)2] or acetamidinate Li[MeC(NiPr)2] afforded the tert-butyl imido complexes Ti(η-C5R4Me)(NtBu){PhC(NSiMe3)2} (R = Me (5) or H (7)) and Ti(η-C5R4Me)(NtBu){MeC(NiPr2)2} (R = Me (6) or H (8)), respectively. Reaction of 6 with ArNH2 or TolNH2 (Ar = 2,6-C6H3Me2, Tol = 4-C6H4Me) afforded the corresponding aryl imido complexes Ti(η-C5Me5)(NR){MeC(NiPr2)2} (R = Ar (9) or Tol (10)). Complexes 5, 7, and 8 underwent cycloaddition/extrusion reactions with CS2 and COS to form μ-sulfido dimers and tBuNCS and tBuNCO, respectively. Compound 6 reacted with COS to form tBuNCO and [Ti(η-C5Me5)(μ-S){MeC(NiPr)2}]2, but with CS2 additional insertion into an amidinate ligand Ti−NiPr bond occurred to form [Ti(η-C5Me5)(μ-S){N(iPr)C(Me)N(iPr)C(S)S}]2. For the aryl imido compounds 9 and 10 the intermediate cycloaddition products Ti(η-C5Me5){N(R)C(E)S}{MeC(NiPr)2} (E = S or O) were observed. No further insertion of CS2 or COS into the Ti−NR bonds occurred. All tert-butyl imido compounds reacted slowly with tBuNCO or ArNCO to form μ-oxo-bridged dimers and tBuNCNtBu or tBuNCNAr, respectively. Reaction of 9 with tBuNCO gave the N,O-bound ureate Ti(η-C5Me5){N(Ar)C(NtBu)O}{MeC(NiPr)2}, which extruded tBuNCNAr to form [Ti(η-C5Me5)(μ-O){MeC(NiPr)2}]2. Reaction of 9 or 10 with aryl isocyanates gave the N,O-bound ureates Ti(η-C5Me5){N(R1)C(NR2)O}{MeC(NiPr)2} (R1 = Ar, R2 = Ar or Tol; R1 = Tol, R2 = Ar or Tol (25)), which did not undergo extrusion. Reaction of 25 with TolNCO gave the net cycloaddition−insertion product Ti(η-C5Me5){OC(NTol)NTolC(NTol)O}{MeC(NiPr)2}. Several heterocumulene cross-coupling cycloaddition−insertion reactions were studied: for example, the sequential reaction of 10 with TolNCO and CO2 gave Ti(η-C5Me5){OC(O)NTolC(NTol)O}{MeC(NiPr)2}. Aryl imides 9 and 10 reacted with TolNCNTol to form the guanidinate complexes Ti(η-C5Me5){N(Tol)C(NTol)N(R)}{MeC(NiPr)2} (R = Ar or Tol). Reaction of 5 and 6 with PhNO gave tBuNNPh and μ-oxo-bridged dimers; the aryl imides 9 and 10 reacted similarly. Ketone and aldehyde CO/TiNR bond metathesis reactions occurred for certain tert-butyl and aryl imido compounds with MeCOMe, PhCOPh, PhCOH, and PhCOMe, and in some instances intermediates were observed. Slow imide/imine metathesis occurred between Ti(η-C5Me5)(N-4-C6H4NMe2){PhC(NiPr2)2} and PhCH(NTol). Compound 6 rapidly converted PhCONH2 and Me(CH2)4CONH2 to the corresponding nitriles, but the analogous reaction with tBuCONH2 was slower. Several other titanium imido compounds and Ti(NMe2)2Cl2 were also evaluated for the PhCONH2 dehydration reaction.