Tricarbonyl molybdenum, reactions with dienes

In contrast to 73, the related tricarbonyl [2-(>/5-cyclopentadienyl)ethyI]-molybdenum (83) (107) forms fairly stable diene complexes with la-Ic in a stepwise reaction, first tj2- and, after prolongated irradiation, -coordinated [Eq. (44)]. Only to a minor extent is insertion of the dienes la and lb into the Mo—C [Pg.338]

Richard followed the course of the reactions of Cr(CO)6 and Mo(CO)6 with hexamethylborazine by UV-vis spectroscopy but although he observed that the intensity of the absorption maximum of the hexacarbonyls at around 290 nm decreased and a new band at around 350 nm appeared, he was unable to identify the new product. Experiments with other starting materials such as norborna-diene chromium and molybdenum tetracarbonyl or tris(aniline) molybdenum tricarbonyl which readily react with arenes by ligand exchange, also failed. The key to success was to use tris(acetonitrile) chromium tricarbonyl as the precursor, which in dioxan under reduced pressure afforded the desired hexamethylborazine chromium tricarbonyl as a stable crystalline solid in 90% yield. This was the breakthrough and, after we had communicated the synthesis and spectroscopic data of the complex in the January issue 1967 of Angewandte Chemie, Richard finished his work and defended his Ph.D. thesis in June 1967. Six months before, in December 1966,1 defended my Habilitation thesis in front of the faculty and became Privatdozent (lecturer) on the 1st of January 1967. 

The cyclodimerization of 3,3-dimethylcyclopropene to form 3,3,6,6-tetramethyl-exo-tri-cyclo[3.1.0.0 ]hexane (4) can also be achieved with pentacarbonyliron in toluene at 95"C in 3 hours (no yield given) or in tetrahydrofuran at 60 °C with catalytic amounts of hexacarbonyl-molybdenum (77% yield, 93% conversion) or hexacarbonyltungsten (86.5% yield). With nonacarbonyldiiron a stoichiometric ring-opening reaction and formation of tricarbonyl(2-methyl-l-propenylketene)iron has been observed (see Section 2.C. for details). A 40% yield of the tricyclic dimer 4 is obtained under the catalytic action of ( / -cycloocta-l,5-diene)(t -cyclopentadienyl)cobalt(I). ... 

Tricarbonyl(6,6-diphenylfulvene)chromium(0) (52) was obtained by reaction of 6,6-diphenylfulvene with hexacarbonylchromium in 64% yield [56]. Later it was shown that almost quantitative yields can be obtained under photochemical reaction conditions starting from (benzene)Cr(CO)3 or from (mesitylene)Cr(CO)3 as the complexation reagent [63]. The corresponding molybdenum and tungsten complexes were prepared by treatment of the ligands with tris(acetonitrile)M(CO)3 (M = Mo, W) [64]. Olefin complex 53 was obtained by Wilkinson and Altman in 51% yield from 6,6-diphenylfulvene and bis(dicarbonylchlororhodium). Similar complexes were prepared with other rhodium reagents [58]. Hiibel and Weiss [59] prepared the diene tri-carbonyliron complex 54 (11-30%) in addition to the dinuclear complex, in which either one of the endocyclic double bonds is coordinated at Fe(CO)4 (49-66%). 

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