New Metallacarborane Chemistry: Molybdenum and Tungsten Carbonyl Multidecker Sandwiches. Cluster Dimers Linked via Metal-Metal Bonds(1).
This article reports the synthesis, characterization, and chemistry of the first molybdenum and tungsten complexes bearing small carborane ligands, including novel M-M-linked dicluster species. The reaction of the nido-2,3-Et(2)C(2)B(4)H(4)(2)(-) dianion with (RCN)(3)M(CO)(3) reagents (M = Mo, W; R = Me, Et) gave the (Et(2)C(2)B(4)H(4))M(CO)(3)(2)(-) anions, which were isolated as lithium (12-crown-4) salts 1b (M = Mo) and 2b (M = W). Treatment of 1b and 2b with Ph(4)PX (X = Cl, Br, I) followed by triflic acid afforded the dimeric products [(Et(2)C(2)B(4)H(4))Mo(CO)(2)](2)(&mgr;-X)(2) (X = Cl (3a), Br (3b), I (3c)) and the corresponding tungsten dimers 4a-c, all of which are red or orange air-stable crystalline solids. X-ray crystallography on 3b revealed a geometry without precedent in small metallacarborane dimers, in which two MC(2)B(4) pentagonal pyramidal clusters are linked via an intercluster metal-metal bond. From NMR and other spectroscopic evidence, the remaining dimeric products 3a, 3c, and 4a-c are proposed to have structures similar to 3b. Decapitation of 3b with HCl/EtOAc in THF gave red solid [(Et(2)C(2)B(3)H(5))Mo(CO)(2)](2)(&mgr;-Br)(2) (5), which is proposed to have two open planar C(2)B(3) end rings and, hence, is a potential building block for linear polymers via deprotonation and metal-ion-stacking reactions. Compound 3b was also generated in a different reaction, involving the nido-Et(2)C(2)B(4)H(5)(-) anion and [Mo(CO)(4)Br](2)[&mgr;-Br](2) which also produced the bis(carboranyl)molybdenum complex (Et(2)C(2)B(4)H(4))(2)Mo(CO)(2) (6), a nearly colorless solid for which a bent sandwich structure is postulated. The reaction of the nido-cobaltacarborane anion CpCo(Et(2)C(2)B(3)H(4))(-) with [Mo(CO)(4)Cl](2)[&mgr;-Cl](2) in toluene gave two isolable products, red CpCo(Et(2)C(2)B(3)H(3))Mo(CO)(4) (7) and dark red [CpCo(Et(2)C(2)B(3)H(3))](2)Mo(CO)(2) (8), which have, respectively, triple-decker and bent-tetradecker sandwich structures based on X-ray crystallographic structure determinations. The reaction of CpCo(Et(2)C(2)B(3)H(4))(-) with [Mo(CO)(4)Br](2)[&mgr;-Br](2) in toluene gave 8 and a known fused-cluster complex Cp(2)Co(2)(Et(4)C(4)B(6)H(6)) (9). Treatment of the CpCo(Et(2)C(2)B(3)H(4))(-) anion with [W(CO)(4)Br](2)[&mgr;-Br](2) afforded red crystalline CpCo(Et(2)C(2)B(3)H(3))W(CO)(4) (10), which on reaction with PhLi followed by Me(3)OBF(4) gave 11, a B(5)-benzyl derivative of 10. X-ray diffraction analyses established triple-decker sandwich structures for both compounds. The new products were characterized by multinuclear NMR, IR, UV-vis, and mass spectroscopy, and elemental analysis, supplemented by electrochemical data on 3b, 8, and 11.
Curtis
Michael A.
MA
Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901.
Houser
Eric J.
EJ
Sabat
Michal
M
Grimes
Russell N.
RN