Syntheses and characterization of the edge-bridged open metallocenes M(C8H11)2 (C8H11 = cyclooctadienyl; M = Ti, V, Cr or Fe) †

Abstract

The reactions of two equivalents of the cyclooctadienyl anion with various divalent transition metal salts (M = Ti, V, Cr or Fe) led to the formation of the appropriate bis(cyclooctadienyl)metal complexes, isolable as crystalline compounds. Their constitutions have been established through NMR and mass spectroscopies, elemental analyses, and single crystal X-ray diffraction studies. As with the M(2,4-C 7 H 11 ) 2 and M(6,6-dmch) 2 (C 7 H 11 = dimethylpentadienyl; dmch = dimethylcyclohexadienyl) complexes, the titanium and vanadium compounds adopt low spin configurations, thereby differing from their metallocene analogs. The structures observed for these complexes in the solid state are similar to those of the M(2,4-C 7 H 11 ) 2 complexes. The low spin titanium complex also forms a mono(ligand) adduct with CO, although the binding appears noticeably weak due to the steric influence of the edge bridge.

Crystal structure of bis(6,6-dimethylcyclohexadienyl)vanadium, V(C8H11)2

“…The conformation angle can be defined as the relative twist between the two dienyl ligands, with a value of 0°corresponding to a fully eclipsed orientation, and 180°to an anti orientation [2]. The value found here, 96.2°, is similar to the values of 89.7°for its cyclooctadienyl analogue [3], and 89.8°for its 2,4-dimethylpentadienyl analogue [4]. These contrast markedly with values for their three iron analogues, with respective conformation angles of 47.5° [5], 58.4° [3], and 59.7° [6].…”

“…The value found here, 96.2°, is similar to the values of 89.7°for its cyclooctadienyl analogue [3], and 89.8°for its 2,4-dimethylpentadienyl analogue [4]. These contrast markedly with values for their three iron analogues, with respective conformation angles of 47.5° [5], 58.4° [3], and 59.7° [6]. Additionally, one observes the expected trends in VC bond distances.…”

Synthesis and reactions of the cyclooctadienylmolybdenum complexes [MoBr(CO)2(NCMe)2(η3-C8H11)] (η3-C8H11 = 1–3-η:4,5-C8H11 or 1–3-η:5,6-C8H11)

“…Although the organometallic chemistry of the cyclooctadienyl ligand is well developed, the majority of reports concern the chemistry of the Fe 11-14 and Co 15-18 triads, together with a few accounts of complexes of Ti, 14 Zr, 19 V, 14 Re, 20 and Ni. 21 Prior to our work in this area, there were no examples of the cyclooctadienyl ligand coordinated to molybdenum or tungsten.…”

“…The series of references ( ref. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] The molecular configurations, annotated with the crystallographic numbering schemes, and a table of important bond lengths and angles (excluding bond lengths and angles of the cylooctadienyl ligand) for 4a, 5a, and 8b are presented in Fig. 1-3, respectively, and Table 1).…”

Synthesis, structure and hapticity interconversion reactions of pentahapto-bonded cyclooctadienyl complexes of molybdenumElectronic supplementary information (ESI) available: 1H and 13C NMR data for [Mo(CO)2(L′)(L2)(η3-C8H11) 8a, 9a 11a, 12a, 3b, 8b, 9b, 10b, 11b, 12b. See http://www.rsc.org/suppdata/dt/b2/b209975f/

“…However, even within the sequence of six-, seven-and eight-membered, edge-bridged systems, there are some significant differences in structure and reactivity as demonstrated by a series of investigations on edgebridged metallocenes and their ligand adducts. [2][3][4][5] Clearly, it is important to understand the role of the edge-bridge and the impact of its size in terms of effects on structure and reactivity and our contribution to this objective centres upon our work with half-sandwich complexes of Mo and W containing the edge-bridged dienyls C 7 H 9 [6][7][8] and C 8 H 11 . 9, 10 The merits of these systems are first, the direct comparability of C 7 H 9 and C 8 H 11 ligands with, in each case, only H substituents attached to the edge-bridge methylene carbons and secondly the ready availability of data for analogous cyclopentadienyl, indenyl 11 and pentadienyl 12-15 complexes for purposes of comparison.…”