Synthesis, X-ray structure, and reactivity with Lewis acids of metallacyclopentane derivatives of rhodium(III) and iridium(III). Observation of the first boron trifluoride-promoted C–H bond activation in transition metal alkyls

Abstract

The metallacyclopentanes [[graphic omitted]H2}(η5-C5Me5)(PPh3)][(1b) M = Rh, R = Me, R′= H; (1c) M = Rh, R = R′= Me; (1e) M = Ir, R = Me, R′= H; (1f) M = Ir, R = R′= Me; (1g) M = Ir, R = Pri, R′= H] were prepared by reacting the appropriate alkylating reagent M′[CH2CH(R)CH(R′)CH2]M′(M′= Li or MgCl) with the dichlorides of formula [MCl2(η5-C5Me5)(PPh3)]. Complexes (1) were characterized by elemental analysis, 1H n.m.r., and mass spectrometry. The X-ray crystal structures of (1c), (1e), and (1f) have been determined. (1c) and (1f) give isostructural P21/c crystals, while (1e) crystallizes in the space group C2/c. The cell constants are: (1c), a= 14.982(9), b= 11.058(6), c= 18.421(10)A, β= 101.13(2)°, Z= 4, R(3 964 reflections, 493 parameters)= 0.0443; (1e), a= 33.63(4), b= 9.29(1), c= 20.56(2)A, β= 116.6(2)°, Z= 8, R(3 196, 476)= 0.0472; (1f), a= 15.01(2), b= 11.10(1), c= 18.44(2)A, β= 100.90(4)°, Z= 4, R(4 136, 446)= 0.0334. All compounds possess a structure of the ‘three-legged piano stool’ type, the major differences lying in the puckering of the metallacyclopentane rings which is larger in the dimethylated derivatives (1c) and (1f) than it is in (1e), where the metallacyclic moiety is rather flattened. The endocyclic Cβ–Cβ, bond in (1e) is 1.34(3)A, while it is 1.51(1) and 1.52(1)A in (1c) and (1f), respectively. The rhoda- and irida-cyclopentanes (1a)(M = Rh, R = R′= H), (1b), (1c), (1d)(M = Ir, R = R′= H), (1e), and (1f) react under very mild conditions, with BF3·Bun2O and with [CPh3][PF6] to give the η3-allyl complexes [M{η3-CH2C(R)C(R′)Me}(η5-C5Me5)(PPh3)][BF4](2) and [M{η3-CH2C(R)C(R′)Me}(η5-C5Me5)(PPh3)][PF6](3)[(a) M = Rh, R = R′= H; (b) M = Rh, R = Me, R′= H; (c) M = Rh, R = R′= Me; (d) M = Ir, R = R′= H; (e) M = Ir, R = Me, R′= H; (f) M = Ir, R = R′= Me], respectively, via the regiospecific hydrogen abstraction from the alkyl-substituted β-carbon atom by Lewis acids. Complexes (2) and (3) were characterized by elemental analysis, 1H n.m.r., and fast atom bombardment mass spectrometry.