Structural studies and matrix photochemistry of tetramethyl-oxorhenium(VI), (CH_3)_4ReO, and related compounds

摘要

The crystal structure of tetramethyloxorhenium(VI), (CH_3)_4ReO, 1, at 150 K reveals molecules with a square-based pyramidal, skeleton and dimensions very similar to those in the gas phase. The realted binuclear compound [(CH_3))3Re(O)]_2O, 2, has likewise been shown to feature rhenium centres with a similar coordination geometry linked by a linear Re-O-Re bridge and carrying terminal Re=O bonds that are mutually trans. Salient average dimensions (distances in A, angles in deg) are as follows: 1 Re-C 2.110(8), Re = O 1.684(4), O=Re-C 112.6(2), C-Re-C 81.5(5) and 134.8(3); 2 Re-C 2.095-2.134(11), Re=O 1.675(6), Re-O 1.851(1), O=Re-C 103.0-113.5(4), C-Re-C 79.2(4) and 132.5-137.0(4). Density functional theory (DFT) calculations have been performed to predit ionization energies for (CH_3)_4ReO. In the light of these results, the photoelectron spectrum has been reassigned. IR spectroscopic measurements have been used to chart the reactions activated by irradiating solid argon matrices doped with 1 with broad-band UV-visible light (200 <= lambda <= 800 nm). The spectra have been interpreted on the basis of additional experiments with (CD_3)_4ReO, 1-d_(12), and by comparison either with the vibrational properties forecast by calculations or with those of known related molecules. Hence photoexcitation is shown to result in the elimination of methane and the formation of the novel methylidene-rhenium(VI) compound H_2C = Re(O)(CH_3)_2, 3. The results are discussed in relation to the photochemistry of methyltrioxorhenium(VII) in similar circumstances.