MOLYBDENUM COMPLEXES WITH HIGHLY ALKYLATED CYCLOPENTADIENYL LIGANDS

Reaction of hexacarbonylmolybdenum with 1,2,3,4-tetraisopropylcyclopentadiene gives [(eta-5-C5iPr4H)Mo(CO)3H] (1), which on treatment with 2,5-norbornadiene is dehydrogenated to [{(eta-5-C5iPr4H)Mo(CO)2}2](Mo = Mo) (2). The mixed-substituted dimolybdenum complex [(eta-5-C5Me5)(CO)2Mo = Mo(CO)2(eta-5-C5iPr4H)] (6) is accessible, e.g., from [(eta-5-C5Me5)Mo(CO)3Cl] and [(eta-5-C5iPr4H)Mo(CO)3]Na (3). Complex 3 yeilds [(eta-5-C5iPr4H)Mo(CO)3Cl] (4) with CuCl2 and [(eta-5-C5iPr4H)Mo(CO)3-SiHMe2] (5) with Me2HSiCl. Low-temperature H-1-NMR spectra of [(eta-5-C5iPr5)Mo(CO)3CH3] (7), synthesized from [(eta-5-C5iPr5)Mo(CO)3]Na and MeI, show the signals of two isomers with different orientation of the isopropyl groups about the five-membered ring. DELTA-G not-equal of isopropyl rotation has been calculated to be 55.6 +/- 4 kJ/mol. [(eta-5-C5H2tBu3-1,2,4)Mo(CO)3]Na reacts with MeI to form [(eta-5-C5H2tBu3-1,2,4)Mo(CO)3CH3] (8).