Structure and Reactivity of Neutral and Cationic trans-N,N′-Dibenzylcyclam Zirconium Alkyl Complexes

Abstract

Reactions of (Bn 2 Cyclam)ZrCl 2 (1) (where Bn 2 Cyclam = trans-N,N 0 (PhCH 2 ) 2 Cyclam) with appropriate alkylating reagents produced (Bn 2 Cyclam)ZrR 2 (R = Me (2), CH 2 Ph (3), n Bu (4), CCPh (5)). Activation of the ortho C-H bond of the two macrocycle benzyl substituents in complexes 2, 3, and 4 was thermally induced, leading to the formation of a bis(ortho-metalated) complex, ((C 6 H 4 CH 2 ) 2 Cyclam)Zr ( 6). This reaction proceeds along with RH elimination and converts the original dianionic tetracoordinated cyclam in a tetraanionic hexacoordinated ligand where two new Zr-C Ph bonds complete the metal sphere. Treatment of 6 with one equivalent of HCtCPh led to ((C 6 H 4 CH 2 )BnCyclam)Zr(CCPh) ( 7) via protonation of one Zr-C Ph bond by phenylacethylene. Further reaction of 7 with an excess of HCtCPh led to 5. The reactions of 2 and 3 with B(C 6 F 5 ) 3 are strongly solvent dependent. Solvent-stabilized cationic species of formula [(Bn 2 Cyclam)ZrR(Solv)]-[RB(C 6 F 5 ) 3 ] were obtained from reactions of 2 in CD 2 Cl 2 (10) or d 8 -THF ( 12) and from 3 in d 8 -THF (9). The reactions of 3 in CD 2 Cl 2 or d 8 -toluene gave [(Bn 2 Cyclam)Zr(η 2 -CH 2 Ph)][ PhCH 2 B(C 6 F 5 ) 3 ] (8). Finally, the reaction of 2 in d 8 -toluene led to [(Bn 2 Cyclam)Zr(C 6 F 5 ){CH 2 B(C 6 F 5 ) 2 }] (14); the precursor of the latter is the zwitterionic [(Bn 2 Cyclam)Zr(CH 3 ){CH 3 B(C 6 F 5 ) 3 }] (11), which then undergoes methane elimination and C 6 F 5 migration from boron to zirconium. The mechanism of this reaction was studied by DFT and revealed that (i) methane elimination is assisted by one alphaagostic C-H bond and (ii) migration of the C 6 F 5 ring is supported by one bridging fluorine bond between the zirconium and one of the C 6 F 5 rings that remains bonded to boron.

Intramolecular hydroamination catalysis using trans-N,N′-dibenzylcyclam zirconium complexes

“…Addition of MgClMe to compound 2 gave the imido derivative 3, upon methane elimination in 68% yield. As reported previously, 5 can be obtained by heating solutions of the bis (alkyl) complex 4 [8].…”

“…Toluene-d 8 and benzene-d 6 were dried with 4 Å molecular sieves, degassed and stored under nitrogen. Literature methods were used to prepare H 2 (Bn 2 Cyclam), (Bn 2 Cyclam)ZrCl 2 , (Bn 2 Cyclam)Zr(CH 2 Ph) 2 , and ((C 6 H 4 CH 2 ) 2 Cyclam)Zr [8,9].…”

“…A pale yellow solid was obtained in 74% yield (0.32 g). 1 H NMR (toluene-d 8 H 7.09,N 11.20. Found: C 61.56,H 7.49,N 11.08.…”

“…The flexibility of the ancillary ligand, already evidenced by its hemiliable behavior [7], as well as its participation in CeH activation reactions [8] are expected to play a prominent role in catalysis. We anticipate that these features are particularly relevant in processes that involve proton exchange as is the case of hydroamination.…”

Synthesis, Structure and Ethylene Polymerization Behavior of Group 4 Metal Complexes Bearing Salicylaldaminato Ligands with Appended Donor Functionality

“…[18] Notably, the three heteroatoms and group 4 metal atom in all structures are co-planar, in which the ligand exhibits a "pincer" like system. [19] For instance, the sum of the angles of O (1) [14,20] The coordinative unsaturation around the metal center is thus compensated by the coordination of the ipso carbon of the benzyl group (all the M-C-Cipso angles are listed in Table 1). Taking 3a for example, one M-C-Cipso angle is 89.1(2)° whereas the other is 112.7(2)°.…”