The role of ligand steric hindrance in determining the stability of very short VV contacts. Preparation and characterization of a series of V (II) and V (III) amidinates

• Published in: Inorganica Chimica Acta 1996-03, Vol.244 (1), p.37-49
• Main Authors: Hao, Shoukang, Berno, Pietro, Minhas, Ravinder K., Gambarotta, Sandro
• Format: Article
• Language: English
• Subjects: Crystal structures; Dinuclear complexes; Formanidinate complexes; Vanadium complexes
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/0020-1693(95)04757-3

The reaction of VCl 2 (TMEDA) 2 and of VCl 3(THF) 3 with two equivalents of formamidinate lithium salts, respectively, yielded dimeric ∗[CyNC(H) NCy] 2V∗ 2 ( 2), with a very short VV multiple bond and ∗[CyNC(H)NCy]∗ 2 ( 4) which is also dimeric. The formation of 2 proceeded through the intermediate monomeric [CyNC (H) NCy] 2 V(TMEDA) ( 1) which was isolated and fully characterized. The dinuclear structure was reversibly cleaved by treatment with pyridine forming the monomeric [CyNC(H)NCy] 2V(Py) 2 ( 3). Conversely, similar reactions with acetamidinate anion gave only the monomeric [CyNC(Me)NCy] 2 V (THF) 2 ( 5a) and [CyNC(Me)NCy] 2VCl ( 7), respectively. Attempts to form a dinuclear structure by either removal of THF from 5a or reduction of 7 gave only the V (III) compound [CyNC(Me)NCy] 3V ( 6). In the case of the very bulky benzamidinate ligand, similar monomeric complexes [Me 3SiNC (Ph) NSiMe 3] 2 V (THF) 2 ( 5c) and [Me 3SiNC(Ph) NSiMe 3] 2 VCl ( 10) were obtained. However, attempts to form dinuclear species via THF dissociation from 5c or reduction of 10 gave a novel dinitrogen complex ∗[Me 3SiNC(Ph)NSiMe 3] 2V∗ 2 ( 8). Crystal data are as follows. 1: C 32H 62N 6V, monoclinic, P2 1/ a, a = 18.085 (3), b = 10.737 (2), c = 18.721 (2) A ̊ , β = 114.37 (4) °, Z = 4; 2: C 52 H 92N 8V 2 , monoclinic, P2 1, a = 11.671 (3), b = 10.371 (2), c = 22.645 (3) A ̊ , β = 100.65 (1)°, Z = 2; 5c: C 34H 62 N 4 Si 4O 2 V , orthorhombic, Pbcn, a = 18.133 (7), b = 12.504 (6), c = 17.428 (4) A ̊ , Z = 4; 6: C 42 H 75 N 6 V , monclinic P2 1/ c , c = 22.777 (4) A ̊ , β = 103.04 (2)°, Z = 4; 7: C 28 H 50 N 4 VCl, triclinic, P-1 , a = 11.132 (4), b = 13.630 (4), c = 10.276 (2) A ̊ α= 95.92 (2), β = 98.38 (2), γ = 109.29 (3) °, Z = 2; 8: C 52H 92N 10V 2Si 8, triclinic, P-1, a = 14.181 (2), b = 18.713 (2), c = 13.257 (2) A ̊ , α = 99.48 (1), β = 94.13(2), γ = 91.87 (2) °, Z = 2; 10: C 26H 46N 4 VClSi 4, triclinic , P-1, a = 12.781 (5), b = 13.128 (4), c = 12.126 (5) A ̊ , α =104.85 (3), β =113.29 (4), γ = 66.80 (4) °, Z = 2.