New single-, double-, and cross-coupling and imido group transfer reactions of cyclopentadienyl-amidinate titanium imido complexes are described. Reaction of Ti(η-C5R4Me)(N t Bu)Cl(py) (R = Me or H) with the lithiated benzamidinate Li[PhC(NSiMe3)2] or acetamidinate Li[MeC(N i Pr)2] afforded the tert-butyl imido complexes Ti(η-C5R4Me)(N t Bu){PhC(NSiMe3)2} (R = Me (5) or H (7)) and Ti(η-C5R4Me)(N t Bu){MeC(N i Pr2)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(N i Pr2)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 t BuNCS and t BuNCO, respectively. Compound 6 reacted with COS to form t BuNCO and [Ti(η-C5Me5)(μ-S){MeC(N i Pr)2}]2, but with CS2 additional insertion into an amidinate ligand Ti−N i Pr bond occurred to form [Ti(η-C5Me5)(μ-S){N( i Pr)C(Me)N( i Pr)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(N i Pr)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 t BuNCO or ArNCO to form μ-oxo-bridged dimers and t BuNCN t Bu or t BuNCNAr, respectively. Reaction of 9 with t BuNCO gave the N,O-bound ureate Ti(η-C5Me5){N(Ar)C(N t Bu)O}{MeC(N i Pr)2}, which extruded t BuNCNAr to form [Ti(η-C5Me5)(μ-O){MeC(N i Pr)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(N i Pr)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(N i Pr)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(N i Pr)2}. Aryl imides 9 and 10 reacted with TolNCNTol to form the guanidinate complexes Ti(η-C5Me5){N(Tol)C(NTol)N(R)}{MeC(N i Pr)2} (R = Ar or Tol). Reaction of 5 and 6 with PhNO gave t BuNNPh and μ-oxo-bridged dimers; the aryl imides 9 and 10 reacted similarly. Ketone and aldehyde CO/TiNR 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(N i P...

No abstract

A combined experimental and DFT study of the reactions of cyclopentadienyl-amidinate titanium imido complexes with CO(2) is reported. Cycloaddition reactions of the aryl imido compounds Ti(eta-C(5)R(4)Me)(NAr){R(2)C(NR(1))(2)} (R = H or Me; R(1), R(2) = SiMe(3), Ph or (i)Pr, Me) with CO(2) gave the corresponding N,O-bound carbamate complexes Ti(eta-C(5)R(4)Me){N(Ar)C(O)O}{R(2)C(NR(1))(2)}. These reacted further with CO(2) by insertion into the Ti-N(Ar) bond to afford the new dicarboxylates Ti(eta-C(5)R(4)Me){OC(O)N(Ar)C(O)O}{R(2)C(NR(1))(2)} in which the original Ti=NAr bond has been completely cleaved. The X-ray structures of two of these have been determined. The CO(2) insertion reactions of the para-substituted phenyl carbamate complexes Ti(eta-C(5)Me(5)){N(-4-C(6)H(4)X)C(O)O}{MeC(N(i)Pr)(2)} (X = Me, CF(3) or NMe(2)) were first order with respect to both carbamate complex and CO(2) and the pseudo first order rate constants were effectively independent of the para substituent. The corresponding tert-butyl imido compounds Ti(eta-C(5)R(4)Me)(N(t)Bu){R(2)C(NR(1))(2)} also reacted with CO(2) to form N,O-bound carbamate complexes, Ti(eta-C(5)R(4)Me){N((t)Bu)C(O)O}{R(2)C(NR(1))(2)}. However, these did not insert a further molecule of CO(2) and instead extruded (t)BuNCO to form the crystallographically characterized oxo-bridged dimers [Ti(eta-C(5)R(4)Me)(mu-O){R(2)C(NR(1))(2)}](2). These reactions proceeded via transient terminal oxo intermediates, one of which was trapped by the addition of TolNCO (Tol = p-tolyl). DFT (B3PW91) calculations on Ti(eta-C(5)H(5))(NR){MeC(NMe)(2)} (R = Me, Ph, 4-C(6)H(4)Me, 4-C(6)H(4)NMe(2), 4-C(6)H(4)CF(3)) reacting with CO(2) showed that the second CO(2) insertion is thermodynamically favoured over isocyanate extrusion, and that the rates of the two processes are similar. Calculations on Ti(eta-C(5)R(5))(N(t)Bu){MeC(N(i)Pr)(2)} (R = H or Me) showed that increasing the steric bulk increases the thermodynamic favourability of the isocyanate extrusion process and significantly raises the activation barrier for the second CO(2) insertion, making the latter process impossible.

No abstract