1398
M.L.H. Green et al. / Polyhedron 24 (2005) 1388–1403
into other positions of the n-pentyl chain was observed
tone, chloroform, dichloromethane and pyridine),
distilled and degassed by the freeze–pump–thaw tech-
nique prior to use. CDFCl2 was prepared by the litera-
ture method [31]. WCl6 (99%), LiAlH4 (95%), LiAlD4
(96%), nD4 Super-Hydrideꢂ LiBEt3H (1.0 M solution
in THF), dimethylzinc (2.0 M solution in hexanes),
1
by H or H NMR spectroscopy.
2
In summary, thermolysis of the n-alkyl-deuteride
compounds [W{(g-C5D4)C(CD3)2(g-C5D4)}{(CH2)n-
CH3)2D}] (n = 1–4) and [W{(g-C5H4)CMe2(g-C5H4)}-
{CD2CD3)H]} shows intramolecular hydrogen/deuterium
exchange between the a-methylene hydrogens of the
n-alkyl ligand and the W–D group. Exchange into other
positions of the n-alkyl ligand was not observed for any
t
diethylzinc (1.0 M solution in hexanes), BuLi (1.7 M
solution in pentane), nBuLi (2.5 M solution in light
petroleum ether (b.p. 40–60 ꢁC)), [Na{AlH2(OCH2-
CH2OCH3)2}] (2.5 M solution in toluene), HCl (1.0 M
solution in diethyl ether), HBF4 (54+ wt% solution in
diethyl ether), NH4I, 1-chloro-n-propane, 1-chloro-n-
butane, 1-chloro-n-pentane, 1-chloro-n-hexane, d5-etha-
nol, pyrrolidine, Me2SiCl2 and D2 were purchased from
Aldrich Chemical Company and used without further
purification. ZnCl2 was bought from Aldrich Chemical
Company and dried in refluxing thionyl chloride for
6 h. Magnesium turnings were preactivated by the addi-
tion of a small amount (ca. 2 wt%) of dibromoethane to
a suspension in THF and then washed with THF.
The compounds [W{(g-C5H4)CMe2(g-C5H4)}Cl2]
[1,2] and [Li{AlD2(OCH2CH2OCH3)2}] [26], were pre-
pared using standard literature methods. NMR spectra
were recorded out on a Varian Unity Plus 500 spectrom-
of
the
compounds
[W{(g-C5D4)C(CD3)2(g-
C5D4)}{(CH2)}nCH3)2D] (n = 1–4). Similarly, H/D
scrambling onto the a-methylene position was also ob-
served by NMR spectroscopy for the d5-ethyl-hydride
compound [W{(g-C5H4)CMe2(g-C5H4)}CD2CD3)2H].
Whereas the methyl-deuteride compound [W{(g-5H4)-
CMe2(g-C5H4)}(CH3)D] is stable at 110 ꢁC, the higher
n-alkyl-deuteride compounds [W{(g-C5D4)C(CD3)2(g-
C5D4)}{(CH2)nCH3)2D]} (n = 1–4) decompose slowly
above ca. 65 ꢁC.
We propose that the H/D exchange into the
a-methylene hydrogens proceeds by an intramolecular
mechanism with an intermediate or transition state
agostic alkane (see Fig. 7) by analogy with H/D the
intermolecular exchange process proposed for the
methyl compound [W{(g-C5H4)C(CH3)2(g-C5H4)}-
CH3D] and related studies [2,3,10–26]. Subsequent to
this work [6] there have been two reports of migration
of transition metal along metal-alkyl chains of the
kind hoped for in these studies [27,28]. Also there
he been an elegant stdy by Ball et al. [29] in which al-
kane-r-transition metal complexes are observed in
solution by NMR studies.
2
eter (1H, H, and 13C spectra were recorded at 499.868,
76.750, and 125.703 MHz, respectively). The spectra
were referenced internally relative to the residual pro-
tio-solvent (1H), residual deutero-solvent (2H) and sol-
vent (13C) resonances relative to tetramethylsilane (1H,
2H, 13C; d = 0 ppm). Chemical shifts (d) are expressed
in ppm and coupling constants (J) in Hz. Mass spectra
(FAB) were recorded by the EPSRC Mass Spectrometry
Service at the University College of Swansea.
IR spectra were recorded on a Mattson Polaris FTIR
spectrometer or a Perkin–Elmer 1710 FTIR spectrome-
ter. Samples were prepared as a Nujol mull between
3. Experimental
All manipulations of air and/or moisture sensitive
materials were performed under an inert atmosphere
of dry dinitrogen using standard Schlenk line techniques
or in an inert atmosphere dry box containing dinitrogen
[30]. Inert gases were purified firstly by passage through
NaCl plates. Data are quoted in cmꢀ1
.
Elemental analysis data were obtained from the
Microanalysis Department of the Inorganic Chemistry
Laboratory, Oxford.
˚
columns filled with activated molecular sieves (4 A) and
3.1. Preparation of [Zn{CD2CD3}2]
then either manganese (II) oxide suspended on vermicu-
lite, for the Schlenk line, or BASF catalyst, for the dry
box. Celiteꢂ filtration aid was purchased from Fluka
Chemie and oven-dried at 100 ꢁC prior to use.
A thick-walled glass tube was charged with a finely
ground mixture of zinc powder (7 g, 107.1 mmol) and
copper powder (1.7 g, 26.8 mmol). Anti-bumping gran-
ules were added and the admixture was dried by heating
under reduced pressure at 200 ꢁC for 2 h. d5-Iodoethane
(7.9 g, 49.1 mmol) was transferred to the tube via low
pressure distillation and the tube was sealed under re-
duced pressure, prior to heating overnight at 140 ꢁC.
The tube was connected to a Schlenk line, carefully
scored and then broken. Volatiles were collected and
the compound [Zn{CD2CD3}2] obtained as an extre-
mely pyrophoric colourless liquid. Yield of [Zn{CD2-
CD3)}2] = 0.55 g, 9%.
˚
Solvents were pre-dried over activated 4 A molecular
sieves and then distilled from Na/K alloy (light petro-
leum ether (b.p. 40–60 ꢁC), diethyl ether, pentane and
DME), from sodium (petroleum ether (b.p. 100–
120 ꢁC) and toluene), from potassium (THF) or from
calcium hydride (acetonitrile, dichloromethane and
TMEDA), under a slow continuous stream of dinitro-
gen. DMSO and d1-methanol were used without drying.
Deuterated NMR solvents were dried over potassium
(benzene, toluene and THF) or calcium hydride (ace-