1484
Organometallics 2009, 28, 1484–1494
Fast Kinetic Studies of the Reactivities of Transient Germylenes in
Methanol and Tetrahydrofuran Solution
Farahnaz Lollmahomed, Lawrence A. Huck, Cameron R. Harrington, Saurabh S. Chitnis,
and William J. Leigh*
Department of Chemistry, McMaster UniVersity, 1280 Main Street West, Hamilton, Ontario,
Canada L8S 4M1
ReceiVed October 27, 2008
Laser flash photolysis techniques have been employed to study the reactivities of dimethylgermylene
(GeMe2), diphenylgermylene (GePh2), and a series of ring-substituted diarylgermylenes (GeAr2) in
methanol (MeOH) and tetrahydrofuran (THF) solution, where the germylenes exist as the corresponding
Lewis acid-base complexes with the O-donor solvents. Dimerization to the corresponding digermene is
a significant mode of decay in THF solution, particularly for the GeMe2-THF complex, though for the
diaryl systems it is slowed dramatically compared to the situation in hexane solution. On the other hand,
dimerization is undetectable in MeOH, where the GeAr2-MeOH complexes decay with pseudo-first-
order kinetics at low laser intensities and lifetimes in the 20-50 µs range; the GeMe2-MeOH complex
exhibits a lifetime of ca. 4 µs under similar conditions. Solvent kinetic isotope effects are consistent with
solvent-catalyzed proton transfer to yield the corresponding alkoxyhydridogermane as the process
responsible for the decay of the germylene-MeOH complexes. Their decay is accelerated by strong
acids and bases such as methanesulfonic acid and sodium methoxide, respectively, which quench the
GePh2-MeOH complex with rate constants of ca. 3 × 109 M-1 s-1 in each case. Kinetic isotope and
substituent effects are consistent with rate-determining protonation at germanium in the reactions with
acid, while the results for methoxide quenching are consistent with the formation of the corresponding
Ar2(MeO)Ge- anion as a discrete intermediate, which has been detected in MeOH solution in one instance.
Reaction of sodium methoxide with the germylene-THF complexes also proceeds rapidly and allows
the detection of the corresponding Ar2(MeO)Ge- anions and determination of rate coefficients for their
protonation by MeOH, for all four of the diaryl systems that were studied. The reactivity of the
GeMe2-THF complex toward sodium methoxide, methanesulfonic and acetic acid, CCl4, oxygen, isoprene,
and 4,4-dimethyl-1-pentene has also been examined.
N-H insertion reactions of these species with alcohols11,19-24
Introduction
and primary or secondary amines.20,22,25-27 Complexes of
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transient silylenes and germylenes with ethers, amines, and other
donors have been detected spectroscopically both in low-
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* Corresponding author. E-mail: leigh@mcmaster.ca.
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10.1021/om8010323 CCC: $40.75
2009 American Chemical Society
Publication on Web 02/09/2009