Photoinduced N-2 loss as a route to long-lived organometallic alkane complexes: A time-resolved IR and NMR study

TY - JOUR

T1 - Photoinduced N-2 loss as a route to long-lived organometallic alkane complexes: A time-resolved IR and NMR study

AU - Calladine, James A.

AU - Torres, Olga

AU - Anstey, Mitch

AU - Ball, Graham E.

AU - Bergman, Robert G.

AU - Curley, John

AU - Duckett, Simon B.

AU - George, Michael W.

AU - Gilson, Amy I.

AU - Lawes, Douglas J.

AU - Perutz, Robin N.

AU - Sun, Xue-Zhong

AU - Vollhardt, K. Peter C.

PY - 2010/11

Y1 - 2010/11

N2 - Photolysis of CpRe(CO)(2)(N-2) in cyclopentane or 2,2-dimethylbutane with a UV lamp via a quartz fibre inserted into the NMR probe allows generation of CpRe(CO)(2)(cyclopentane) and CpRe(CO)(2)(2,2-dimethylbutane). The latter is observed in three isomeric forms according to the site of co-ordination to the rhenium. The major isomer, CpRe(CO)(2)(2,2-dimethylbutane-eta(2)-C-1,H-1), exhibits a H-1 NMR resonance for the co-ordinated hydrogen at delta = -2.19 with (1)J(C-H) = 118 Hz. The photochemistry of Cp double dagger Re(CO)(2)(N-2) (Cp double dagger = eta(5)-1,2-C5H3(Bu-1)2) in alkane solution is also reported. Two new organometallic alkane complexes, Cp double dagger Re(CO)(2)(alkane) (alkane = cyclopentane, n-heptane) have been characterized by IR spectroscopy following irradiation of Cp double dagger Re(CO)(2)(N-2) and their rate constants for reaction with CO have been determined. The reaction with cyclopentane has also been studied by NMR spectroscopy at 190 K with in situ laser irradiation at 355 nm. Cp double dagger Re(CO)(2)(c-C5H10) is shown to exhibit the characteristic features of an alkane complex in the NMR spectrum, viz, a large isotopic shift of the H-1 resonance at delta = -2.44 upon partial deuteration of the alkane (Delta delta = 1.77 ppm), a large (1)J(C-H) (114 Hz) and a large negative C-13 chemical shift (delta = -33.8). We find no evidence for CO loss or agostic interactions of the t-butyl groups under these conditions. Cp double dagger Re(CO)(2)(alkane) has a slightly shorter lifetime (ca. 5x) than CpRe(CO)(2)(alkane) for a given alkane. Photolysis of CpRe(CO)(2)(N-2) to form the organometallic alkane complex occurs with a much higher yield than for CpRe(CO)(3). Efficient photoejection of N-2 from Cp double dagger Re(CO)(2)(N-2) is observed upon either 266 or 355 nm laser irradiation. A dinitrogen precursor allows for the use of longer wavelength irradiation and the generation of a higher concentration of the alkane complex following each laser pulse.

AB - Photolysis of CpRe(CO)(2)(N-2) in cyclopentane or 2,2-dimethylbutane with a UV lamp via a quartz fibre inserted into the NMR probe allows generation of CpRe(CO)(2)(cyclopentane) and CpRe(CO)(2)(2,2-dimethylbutane). The latter is observed in three isomeric forms according to the site of co-ordination to the rhenium. The major isomer, CpRe(CO)(2)(2,2-dimethylbutane-eta(2)-C-1,H-1), exhibits a H-1 NMR resonance for the co-ordinated hydrogen at delta = -2.19 with (1)J(C-H) = 118 Hz. The photochemistry of Cp double dagger Re(CO)(2)(N-2) (Cp double dagger = eta(5)-1,2-C5H3(Bu-1)2) in alkane solution is also reported. Two new organometallic alkane complexes, Cp double dagger Re(CO)(2)(alkane) (alkane = cyclopentane, n-heptane) have been characterized by IR spectroscopy following irradiation of Cp double dagger Re(CO)(2)(N-2) and their rate constants for reaction with CO have been determined. The reaction with cyclopentane has also been studied by NMR spectroscopy at 190 K with in situ laser irradiation at 355 nm. Cp double dagger Re(CO)(2)(c-C5H10) is shown to exhibit the characteristic features of an alkane complex in the NMR spectrum, viz, a large isotopic shift of the H-1 resonance at delta = -2.44 upon partial deuteration of the alkane (Delta delta = 1.77 ppm), a large (1)J(C-H) (114 Hz) and a large negative C-13 chemical shift (delta = -33.8). We find no evidence for CO loss or agostic interactions of the t-butyl groups under these conditions. Cp double dagger Re(CO)(2)(alkane) has a slightly shorter lifetime (ca. 5x) than CpRe(CO)(2)(alkane) for a given alkane. Photolysis of CpRe(CO)(2)(N-2) to form the organometallic alkane complex occurs with a much higher yield than for CpRe(CO)(3). Efficient photoejection of N-2 from Cp double dagger Re(CO)(2)(N-2) is observed upon either 266 or 355 nm laser irradiation. A dinitrogen precursor allows for the use of longer wavelength irradiation and the generation of a higher concentration of the alkane complex following each laser pulse.

KW - HYDROGEN BOND ACTIVATION

KW - NOBLE-GAS COMPLEXES

KW - C-H ACTIVATION

KW - ROOM-TEMPERATURE

KW - OXIDATIVE ADDITION

KW - TRANSITION-METALS

KW - FLASH-PHOTOLYSIS

KW - SPECTROSCOPY

KW - PHOTOCHEMISTRY

KW - REACTIVITY

UR - http://www.scopus.com/inward/record.url?scp=79951827786&partnerID=8YFLogxK

U2 - 10.1039/c0sc00311e

DO - 10.1039/c0sc00311e

M3 - Article

SN - 2041-6520

VL - 1

SP - 622

EP - 630

JO - Chemical Science

JF - Chemical Science

IS - 5

ER -