Monomeric Bis(η²-alkyne) Complexes of Copper(I) and Silver(I) with η¹-Bonded Alkyl, Vinyl, and Aryl Ligands

Abstract

Two synthetic routes to compounds [(η5-C5H4SiMe3)2Ti(C⋮CSiMe3)2]MR (abbreviated as [1·MR]; M = Cu: R = Me (5), CH2SiMe3 (6), Et (7), nBu (8), C(H)CH2 (9), C6H2Me3-2,4,6 (13), C6H4Me-4 (14), C6H4OMe-4 (15), C6H4NMe2-4 (16), C6H5 (17); M = Ag: R = C6H2Me3-2,4,6 (18)) are described. These compounds contain monomeric MR entities, which are η2-bonded by both alkyne ligands of the organometallic 3-titanio-1,4-pentadiyne [(η5-C5H4SiMe3)2Ti(C⋮CSiMe3)2] (1). The X-ray structures of 5, 13, and 18 have been solved. Crystals of 5 are monoclinic, space group C2/c, with a = 19.477(1) Å, b = 10.3622(6) Å, c = 16.395(1) Å, β = 95.287(5)°, V = 3294.8(3) Å3, Z = 4, and final R = 0.030 for 3232 reflections with F ≥ 4σ(F) and 240 parameters. Crystals of 13 are orthorhombic, space group Pbcn, with a = 12.4290(9) Å, b = 19.8770(8) Å, c = 15.532(1) Å, V = 3837.2(4) Å3, Z = 4, and final R = 0.026 for 3082 reflections with I ≥ 2.5σ(I) and 217 parameters. The mesitylcopper compound 13 is isostructural with the mesitylsilver compound 18, and crystals of 18 are orthorhombic, space group Pbcn, with a = 12.47(3) Å, b = 20.00(3) Å, c = 15.53(3) Å, V = 3873(13) Å3, Z = 4, and final R = 0.055 for 2068 reflections with I ≥ 2.5σ(I) and 188 parameters. All compounds contain a monomeric bis(η2-alkyne)M(η1-R) unit (M = Cu or Ag) in which the group 11 metal atom is trigonally coordinated by the bis(η2-alkyne) chelate 1 and an η1-bonded monoanionic organic ligand. A bonding description of the bis(η2-alkyne)M(η1-R) entity (M = Cu, Ag) is discussed. The alkylcopper compounds 5−8 decompose in solution either via nucleophilic substitution of one SiMe3 group in 1 to eliminate RSiMe3 or via β-hydride elimination (7 and 8) to eliminate the corresponding alkene, whereas arylcopper compounds 14−17, which lack ortho-substituents rearrange in solution via addition of the monomeric arylcopper entity to one of the alkynes within [1·CuR] to yield unstable 1,1-bimetallaalkene complexes. When R is the monoanionic terdentate ligand {C6H3(CH2NMe2)2-2,6}, the coordination complex [1·CuR] is not isolated, while the corresponding addition product is favored. The X-ray structure of [(η5-C5H4SiMe3)2Ti(C⋮CSiMe3){μ-CC(SiMe3)(R)}Cu], 22, which is a rare example of a 1,1-bimetallaalkene, has been solved. Crystals of 22 are pseudomerohedrally twinned and monoclinic, space group P21/c, with a = 31.05(2) Å, b = 14.323(3) Å, c = 20.014(8) Å, β = 108.53(5)°, V = 8440(7) Å3, Z = 8, and final R = 0.1233 for 8564 reflections with F > 4σ(F) and 462 parameters.