Transition Metal Coordinated Al(X)L₂and Ga(X)L₂Fragments

Abstract

Carbonylmetalate dianions react in thf with the group 13 chlorides X m ECl 3 - m ( E = Al, Ga; X = Cl, Me, Et, i Bu; m = 0, 1) to yield the monoanionic species [(CO) n M−EX m Cl 2 - m ] - (M = Fe, Cr, Mo, W; n = 4, 5) as the primary products which could be isolated as solvent free salts after exchange with a non coordinating cation. After addition of a chelating Lewis base, e.g., tmeda, dme, and solvent exchange with dichloromethane the primary products undergo a second salt elimination reaction, yielding the neutral intermetallic systems (CO) n M−Ga[X(L) 2 ] (M = Cr, Mo, W, Fe; n = 4, 5; X = Cl, Me, Et; L 2 = tmeda, dme, bipy, t Bu-dab, thf 2 ) ( 1 − 14 ) and (CO) 5 M-Al[X(L) 2 ] (M = Cr, Mo, W; X = Cl, Et, i Bu; L 2 = tmeda, tmpda) ( 15 − 20, 23, 24 ). The chloro derivatives can be converted to the corresponding hydrido or tetrahydridoboranato species which is exemplarily shown by compounds 21 and 22 . In the case of R 2 GaCl (R = Me, Et; 2 equiv) as starting compounds a ligand exchange reaction, generating GaR 3, occurs, before the second salt elimination takes place. The new intermetallic systems were characterized by means of elemental analysis and IR, Raman, NMR, and mass spectroscopy. The complexes (CO) 5 Cr−Ga[Cl(tmeda)] ( 2 ), (CO) 5 W−Al[Et(tmeda)] ( 20 ), and (CO) 5 W−Al[Cl(tmpda)] ( 23 ) are also characterized by single-crystal X-ray diffraction. Compounds 2 and 20 crystallize in the monoclinic space group P 2 1 / n, Z = 4. 2: a = 9.059(4) Å, b = 16.084(7) Å, c = 11.835(6) Å, β = 80.6(1)°, V = 1701(1) Å 3, and R = 0.037 ( R w = 0.118). 20: a = 8.606(2) Å, b = 16.463(6) Å, c = 12.469(4) Å, β = 93.88(2)°, V = 1762(6) Å 3, and R = 0.027 ( R w = 0.065). Complex 23 crystallizes in the orthorhombic space group Pccn, a = 23.990(6) Å, b = 9.044(3) Å, c = 15.871(4) Å, V = 3445(1) Å 3, and R = 0.044 ( R w = 0.088). Ab initio quantum chemical calculations at the MP2 level of theory of the model complexes (CO) 5 W−E[Cl(NH 3 ) 2 ] ( E = B, Al, Ga, In, Tl), (CO) 5 W−Al[H(NH 3 ) 2 ], (CO) 5 W−AlH, and (CO) 5 W−AlCl are reported. The group-13 fragments E(R)L 2 behave as strong σ-donors with significant acceptor capabilities. The W−E bonds are strong semipolar covalent bonds with large ionic contributions ( D e (calc) between 70 and 120 kcal/mol). Only the W−Tl bond is comparatively weak ( D e (calc) = 48 kcal/mol).