Organic Matrix Photochemical Studies of Rhenacarborane Nitrosyl Complexes. Evidence for Linkage Isomeric Nitrosyl Photointermediates

Abstract

The photochemistry of the rhenacarborane nitrosyl compounds [1,2-R2-3,3-(CO)2-3-NO-closo-3,1,2-ReC2B9H9], where R = H, I, and R = Me, II, has been studied in Nujol and methytetrahydrofuran (MeTHF) frozen glasses at ca. 90 K. Visible light photolysis gives rise to a new species that has been assigned to the isonitrosyl linkage isomer, while ultraviolet photolysis gives rise to a second species believed to be the η2-NO linkage isomer. In MeTHF high-energy photolysis also gives rise to a CO-loss product. Photolysis of derivatives of I, [3-L-3-L‘-3-NO-closo-3,1,2-ReC2B9H11], where L = CO, L‘ = PMe3, III; L = CO, L‘ = CNC6H3Me2-2, 6, IV, and L = L‘ = CNC6H3Me2-2,6, V, all give rise to a photoproduct believed to be the η2-NO lnkage isomer. There was no evidence of the isonitrosyl isomer in these cases. Complexes III and IV also undergo CO loss. Ultraviolet photolysis of [3,3,3-(CO)3-closo-3,1,2-RuC2B9H11], VI, in MeTHF results in CO loss and formation of the corresponding [3,3-(CO)2-3-MeTHF-closo-3,1,2-RuC2B9H11] derivative. In frozen Nujol, ultraviolet photolysis of VI gives rise to a CO-loss species. Upon visible light back-photolysis or annealing of the sample, this photoproduct gives rise to a second dicarbonyl species of unknown structure.

Luminescent Metallacarboranes

“…[25] Thus at k irr ! 400 nm isomeric conversion to the oxygen-bound terminal NO was observed, while further photolysis at 350 nm < k irr < 400 nm yielded a side-on bound g 2 -NO, both processes being reversible (Scheme 1).…”

3 Boron

“…99 The photochemistry of the rhenacarborane nitrosyl compounds [1,2-R 2 -3,3-(CO) 2 -3-NO-3,1,2-ReC 2 B 9 H 9 ] has been studied affording linkage isomers and η 2 -nitrosyls as photointermediates. 100 Various C cage -substituted analogues of [(η 5 -N(Me) 2 C 4 H 4 )Co-closo-C 2 B 9 H 10 ] have been synthesised and structurally characterised. Solution NMR studies show that intramolecular interactions between the pyrollyl group and cage substituent result in the isolation of a single rotamer.…”

Similar luminescent behavior in an established rhenacarborane complex, [3,3-(CO)2-3-NO-closo-3,1,2-ReC2B9H11] and a new complex anion, [3,3,3-(CO)3-8-I-closo-3,1,2-ReC2B9H10]–

“…Since the lower intensity absorptions have been attributed to nitrosyl reorientations to give species 2c and 2d [4], the higher energy excitation is assigned to a Re I -NO + MLCT transition, as described in the cyclopentadienide analog [Re(NO)(CO) 2 (Z 5 -C 5 H 5 )][PF 6 ] [8]. The photoluminescence excitation and emission spectra of 2a measured in MeTHF at 77 K are shown in Fig.…”

“…The synthesis and spectroscopic characterization of the complex [3,3-(CO) 2 -3-NO-closo-3,1,2-ReC 2 B 9 [3]. While some critical photophysical data for solutions of the complexes 2 have been disclosed, notably the IR-photoanalysis by Bitterwolf et al of the nitrosyl ligand dynamics in low-temperature matrix-isolated complex 2b [4], we reveal herein one of the first reports of visible light emission from a d-block metallacarborane, where the chromophore comprises an endopolyhedral polyhedral skeletal electron (PSE)-contributing metal vertex. We also report herein a related new complex anion, [3,3,3-(CO) 3 -8-I-closo-3,1,2-Re-C 2 B 9 H 10 ] À (3), which is emissive in MeTHF at 77 K. Hawthorne et al have recently reported, albeit weak, stereogenerated luminescence from a nickelacarborane sandwich complex [3,3 0 ,1,1 0 ,2,2 0 -commo-Ni(C 2 B 9 H 11 ) 2 ] and its derivatives with cage carbon substituents [5].…”

“…The UV-vis absorption spectra of solutions of 2a have been previously reported [l max ðÞ ¼ 355ð500Þ; 420 nm (200 M À1 cm À1 )] [4], although we note an additional, intense absorption at 250 nm (7700 M À1 cm À1 ) [7]. Since the lower intensity absorptions have been attributed to nitrosyl reorientations to give species 2c and 2d [4], the higher energy excitation is assigned to a Re I -NO + MLCT transition, as described in the cyclopentadienide analog [Re(NO)(CO) 2 (Z 5 -C 5 H 5 )][PF 6 ] [8].…”