RESUMO
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.
RESUMO
Reactions of Ti(NMe(2))(2)Cl(2) with a wide range of primary alkyl and arylamines RNH(2) afforded the corresponding 5-coordinate imido titanium compounds Ti(NR)Cl(2)(NHMe(2))(2) (R = (t)Bu (1), (i)Pr (2), CH(2)Ph (3), Ph (4), 2,6-C(6)H(3)Me(2) (5), 2,6-C(6)H(3)(i)Pr(2) (6), 2,4,6-C(6)H(2)F(3) (7), 2,3,5,6-C(6)HF(4) (8), C(6)F(5) (9), 4-C(6)H(4)Cl (10), 2,3,5,6-C(6)HCl(4) (11), 2-C(6)H(4)CF(3) (12), 2-C(6)H(4)(t)Bu (13)). The compounds 1-13 are monomeric in solution but in the solid state form either N-H...Cl hydrogen bonded dimers or chains or perfluorophenyl pi-stacked chains, depending on the imido R-group. The compound 13 was also prepared in a "one-pot" synthesis from RNH(2) and Ti(NMe(2))(4) and Me(3)SiCl. Reaction of certain Ti(NR)Cl(2)(NHMe(2))(2) compounds with an excess of pyridine afforded the corresponding bis- or tris-pyridine analogues [Ti(NR)Cl(2)(py)(x)](y) (x = 3, y = 1; x = y = 2), and the structure of Ti(2)(NC(6)F(5))(2)Cl(2)(mu-Cl)(2)(py)(4) shows pi-stacking of perfluorophenyl rings. Reaction of Ti(NMe(2))(2)Cl(2) with cross-linked aminomethyl polystyrene gave quantitative conversion to the corresponding solid-supported titanium imido complex. This paper represents the first detailed study of how supramolecular structures of imido compounds may be influenced by simple variation of the imido ligand N-substituent.
RESUMO
Reactions of zirconium dialkyl- or bis(amido)-dichloride complexes "[Zr(CH2SiMe3)2Cl2(Et2O)2]" or [Zr(NMe2)2Cl2(THF)2] with primary alkyl and aryl amines are described. Reaction of "[Zr(CH2SiMe3)2Cl2(Et2O)2]" with RNH2 in THF afforded dimeric [Zr2(mu-NR)2Cl4(THF)4](R=2,6-C6H3iPr2 (1), 2,6-C6H3Me2 (2) or Ph (3)), [Zr2(mu-NR)2Cl4(THF)3](R=tBu (5), iPr (6), CH2Ph (7)), or the "ate" complex [Zr2(mu-NC6F5)2Cl6(THF)2{Li(THF)3}2](4, the LiCl coming from the in situ prepared "[Zr(CH2SiMe3)2Cl2(Et2O)2]"). With [Zr(NMe2)2Cl2(THF)2] the compounds [Zr2(mu-NR)2Cl4(L)x(L')y](R=2,6-C6H3iPr2 (8), 2,6-C6H3Me2 (9), Ph (10) or C6F5 (11); (L)x(L')y=(NHMe2)3(THF), (NHMe2)2(THF)2 or undefined), [Zr2(mu-NtBu)2Cl4(NHMe2)3] (12) and insoluble [Zr(NR)Cl2(NHMe2)]x(R=iPr (13) or CH2Ph (14)) were obtained. Attempts to form monomeric terminal imido compounds by reaction of or with an excess of pyridine led, respectively, to the corresponding dimeric adducts [Zr2(mu-2,6-C6H3Me2)2Cl4(py)4] (15) and [Zr2(mu-NtBu)2Cl4(py)3] (16). The X-ray structures of 1, 2, 4, 8, 12 and 15 have been determined.