Synthesis, Structure, and Unusual Reactivity of the First Norbornene Carbonyl Complexes of Tungsten

Abstract

Two new norbornene complexes of tungsten(0), W(CO) 5 (η 2 -C 7 H 10 ) (1) and trans-W(CO) 4 -(η 2 -C 7 H 10 ) 2 (2), have been obtained and characterized by IR and NMR spectroscopy, and initial studies of their reactivity are reported here. The molecular structure of compound 1, relatively unstable in solution, was established by single-crystal X-ray diffraction studies. Complex 1 can, depending on reaction conditions, give rise to different types of reactions: in a pure polychloromethane solution, it transforms to a species initiating the ring-opening metathesis polymerization of norbornene (ROMP), whereas in the presence of alcohol (ca. 1%), it leads to catalytic C-C bond formation with selective addition of polychloromethane to the olefinic bond of norbornene. The two-electron chemical oxidation of stable trans-W(CO) 4 -(η 2 -C 7 H 10 ) 2 (2) by SnCl 4 gives a very labile norbornene complex of tungsten(II) (3). The latter compound decomposes in CDCl 3 solution to give chloronorbornane, whereas in benzene-d 6 or toluene-d 8 solution the products of the hydroarylation of norbornene are formed. The identities of the organometallic and organic products were established by IR, NMR, ESI-MS, and GC-MS studies.

A new synthetic route to pentacarbonylalkene complexes of tungsten(0): X-ray crystal structure of [W(CO)5(η2-C2H4)]

“…The crystal structure of [W(CO) 5 (g 2 -C 2 H 4 )](1) has been established by X-ray diffraction studies.To explain the role of g 2 -olefin ligands during the initiation of catalytic reactions by group 6 metal carbonyls, many efforts have been concentrated on the study of olefin-carbonyl complexes [1][2][3][4]. The coordination of an olefin to a transition metal effected in removing electron density from the C@C double bond of olefin.…”

“…Separation of trans-bis(olefin) compounds was achieved due to their high stability. In a slowly evaporated alkane solution, the pentacarbonyl compound decomposes, leaving a stable enough trans-bis(olefin) species [4,7,8]. Only in a few cases has it been possible to isolate and fully characterize the pentacarbonylolefin complexes [4,7,[14][15][16].…”

“…As the result, the olefin ligand can be then easily transformed in catalytic reaction. All group 6 metal carbonyls have been shown to undergo reactions with olefin either by thermal substitution of ligands such as tetrahydrofuran, acetone, or acetonitrile [5] or, recently more frequently, by photochemical substitution of carbonyl ligands in hexacarbonyls [4,[6][7][8].…”

“…Photolysis of an alkane solution of M(CO) 6 (M = Cr, M, W) and olefin leads first to the formation of a thermally labile [M(CO) 5 (g 2 -olefin)] complex and after further irradiation to a much more stable trans-[M(CO) 4 (g 2 -olefin) 2 ] complex [4,[6][7][8][9][10]. Even prolonged irradiation of M(CO) 6 in the presence of olefin gives a mixture of penta-and tetra-carbonyl compounds.…”

“…In a slowly evaporated alkane solution, the pentacarbonyl compound decomposes, leaving a stable enough trans-bis(olefin) species [4,7,8]. Only in a few cases has it been possible to isolate and fully characterize the pentacarbonylolefin complexes [4,7,[14][15][16]. The first one to be isolated and stable enough to be handled at room temperature was the cis-cyclooctene (c-COE) complex [Cr(CO) 5 (g 2 -c-COE)] [14]; subsequently, [Cr(CO) 5 (g 2 -C 2 H 4 )] [15], [W(CO) 5 (g 2 -c-COE)] [16], [W(CO) 5 (g 2 -t-COE)] (t-COE = trans-cyclooctene) [7] and [W(CO) 5 has been obtained and its unusual reactivity towards olefins developed [17] (Scheme 1).…”