ISSN:
0009-2940
Keywords:
Molybdenum heterocycles
;
P - P bonds
;
Activated alkynes
;
Sulfur
;
Insertion reactions
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The insertion of the alkynes ZC≡CZ (2a-i) [Z = Co2R: R = Me (a), Et (b), nPr (c), iPr (d), nBu (e), tBu (f), neo-Pent (g), cyc-Hex (h); Z = CF3 (i)] into the P1-P2 bond of the diphos-phamolybdacyclopropane Mes (1) (Mes = 2,4,6-trimethylphenyl) results in the formation of the diphosphamolybdacyclopentenes Mes (3a-i). According to an X-ray structural analysis, 3a crystallizes in the space group P21/c with the mesityl function at P2 and the cyclopentadienyl fragment at the metal atom on the opposite side of the planar five-membered ring. The same orientation is found in solution by NMR experiments (NOE; 2D 1H, 13C HETCOR). Kinetic investigations confirm that the rate constants decrease in the sequence R = Me 〉 Et 〉 nPr 〉 isoProp 〉 Cy 〉 nBu 〉 neo-Pent 〉 tBu. The second-order reaction and the strongly negative activation entropy which was determined in the case of the reaction 1 + 2e → 3e are consistent with a nucleophilic attack of P2 at one of the triply bonded carbon atoms of the alkyne. The reaction of 3a, h with sulfur affords the diastereomeric compounds Mes (4a, h). An X-ray structural analysis of the heterocycle 4h, which crystallizes in the space group P1, shows the presence of the enantiomeric pair SR/RS. The reaction of 1 with alkynes is hindered if this heterocycle is oxidized by sulfur to give Mes (5). Further reaction of 5 with sulfur leads to the ring-expanded heterocyclic intermediate (6) which crystallizes in the space group P1. The five-membered ring in 6 has an envelope conformation. Upon thermally induced cleavage of the P2S2Mes fragment from 6 the three-membered ring (7) is formed as the final product.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19951281003
Permalink
