Zirconium-catalyzed heterodehydrocoupling of primary phosphines with silanes and germanes

Article abstract of DOI:10.1021/ic7013144

Triamidoamine-supported zirconium complexes catalyze the heterodehydrocoupling of primary phosphines with silane and germanes. In this catalysis, P-Si or P-Ge products are observed exclusively with no competitive P-P bond formation. Phosphido complexes (N

Full text of DOI:10.1021/ic7013144

Inorg. Chem. 2007, 46, 6855−6857
Zirconium-Catalyzed Heterodehydrocoupling of Primary Phosphines with
Silanes and Germanes
Andrew J. Roering,† Samantha N. MacMillan,‡ Joseph M. Tanski,‡ and Rory Waterman*,†
Department of Chemistry, UniVersity of Vermont, Burlington, Vermont 05405, and
Department of Chemistry, Vassar College, Poughkeepsie, New York 12604
Received July 3, 2007
Triamidoamine-supported zirconium complexes catalyze the het-
erodehydrocoupling of primary phosphines with silane and ger-
phosphines with silanes and germanes to form P-Si and
P-Ge bonds. This catalysis is, to the best of our knowledge,
the first instance of high-yielding heterodehydrocoupling
involving primary phosphines, though dimethyltitanocene has
been shown to heterodehydrocouple secondary phosphines
with primary or secondary silanes.5 The use of primary
phosphines herein is advantageous, avoiding transmetalation
or additional reduction steps to form P-H and Si-H/Ge-H
bonds in conventional stoichiometric syntheses of silyl- or
germylphosphines.6
manes. In this catalysis, P
exclusively with no competitive P
complexes (N3N)ZrPHR (N3N
−Si or P−Ge products are observed
−
P bond formation. Phosphido
3
)
N(CH2CH2NSiMe3)3 -, R
)
Ph,
2; Cy, 3) were observed to be the catalyst resting state, and
complex 2 was structurally characterized.
Catalytic dehydrocoupling is a powerful and atom-
economical strategy for the formation of element-element
bonds.1 This kind of catalysis has become a useful surrogate
for the Wu¨rst-type reductions of halogen-substituted group
14 and 15 elements, including phosphorus, and several
families of catalysts that effect dehydrocoupling of phos-
phines have been developed.2 However, catalysts that engage
in heterodehydrocoupling reactions involving phosphines are
far less common, though an increased demand for catalytic
reactions that produce phosphorus-element bonds is emerg-
ing.3,4 We wish to report that complexes of the type (N3N)-
ZrR (N3N ) N(CH2CH2NSiMe3)33-, R ) Me, 1; PHPh, 2;
PHCy, 3) are catalysts for the dehydrocoupling of primary
Two other instances of phosphine heterodehydrocoupling
are known. A variety of simple metal derivatives, including
Rh(I), form P-B bonds via dehydrocoupling of phosphine-
boranes.7 Catalytic P-S bond formation has been observed
with a rhodium bisphosphine catalyst.4
Recently, triamidoamine-supported zirconium complexes
have been shown to catalytically dehydrocouple primary and
secondary phosphines.8 It was observed that in the reaction
of 1 with an equimolar mixture of excess CyPH2 (Cy )
cyclohexyl) and PhPH2, the phenylphosphido derivative, 2,
was formed exclusively. Interestingly, a modest selectivity
for the heterodehydrocoupling product, CyHP-PHPh, was
observed over (RPH)2 (R ) Ph, Cy) under catalytic condi-
tions.8 Seeking to exploit this selectivity, heterodehydrocou-
pling reactions of primary phosphines with silanes and
germanes have been explored.
* To whom correspondence should be addressed. E-mail:
rory.waterman@uvm.edu.
† University of Vermont.
‡ Vassar College.
(1) Gauvin, F.; Harrod, J. F.; Woo, H. G. AdV. Organomet. Chem. 1998,
Reaction of PhPH2 with PhSiH3, TolSiH3 (Tol ) p-tolyl),
and PhMeSiH2 proceeded smoothly in the presence of 5 mol
% of complex 1 or 2 at 90 °C to give the secondary
silylphosphine product with liberation of hydrogen (Table
1). Only minor byproducts were observed (<5%), and the
42, 363-405.
(2) Masuda, J. D.; Hoskin, A. J.; Graham, T. W.; Beddie, C.; Fermin, M.
C.; Etkin, N.; Stephan, D. W. Chem. Eur. J. 2006, 12, 8696-8707
and references therein.
(3) (a) Wicht, D. K.; Glueck, D. S. In Catalytic Heterofunctionalization;
Togni, A., Grutzmacher, H., Eds.; Wiley-VCH: Weinheim, 2001; pp
143-170. (b) Deprele, S.; Montchamp, J.-L. J. Am. Chem. Soc. 2002,
124, 9386-9387. (c) Levine, A. M.; Stockland, R. A., Jr.; Clark, R.;
Guzei, I. Organometallics 2002, 21, 3278-3284. (e) Jin, Z.; Lucht,
B. L. J. Am. Chem. Soc. 2005, 127, 5586-5595. (f) Delacroix, O.;
Gaumont, A. C. Curr. Org. Chem. 2005, 9, 1851-1882. (g) Hirai,
T.; Han, L.-B. J. Am. Chem. Soc. 2006, 128, 7422-7423. (g) Ha¨nisch,
C.; Hampe, O.; Weigend, F.; Stahl, S. Angew. Chem., Int. Ed. 2007,
46, 4775-4779. (h) Blank, N. F.; Moncarz, J. R.; Brunker, T. J.;
Scriban, C.; Anderson, B. J.; Amir, O. Glueck, D. S.; Zakharov, L.
N. Golen, J. A.; Incarvito, C. D.; Rheingold, A. L. J. Am. Chem. Soc.
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M. S.; Hitchcock, P. B.; Procopiou, P. A. Organometallics 2007, 26,
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(5) Shu, R.; Hao, L.; Harrod, J. F.; Woo, H.-G.; Samuel, E. J. Am. Chem.
Soc. 1998, 120, 12988-12989.
(6) (a) Aitken, R. A. In ComprehensiVe Organic Functional Group
Transformations II; Katritzky, A. R., Taylor, R. J. K., Eds.; Elsevier:
Amsterdam, 2005; Vol. 4, pp 539-573. (b) Thornton, P. Sci. Synth.
2003, 5 101-103. (c) Pietruszka, J. Sci. Synth. 2002, 4 473-480. (d)
Fritz, G.; Scheer, P. Chem. ReV. 2000, 100, 3341-3402.
(7) (a) Dorn, H.; Singh, R. A.; Massey, J. A.; Nelson, J. M.; Jaska, C. A.;
Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2000, 122, 6669-6678.
(b) Jaska, C. A.; Manners I. In Inorganic Chemistry in Focus II; Meyer,
G., Naumann, D., Wesemann, L., Eds.; Wiley-VCH Verlag GmbH
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(8) Waterman, R. Organometallics 2007, 26, 2492-2494.
10.1021/ic7013144 CCC: $37.00
Published on Web 07/25/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 17, 2007 6855

COMMUNICATION
Table 1. Results of Dehydrocoupling Reactions with Catalytic
(N3N)ZrMe (1)a
phosphine
substrate
product(s)b
timec
yieldd
PhPH2
PhPH2
PhPH2
CyPH2
PhSiH3
PhH2Si-PHPh
3
3
6
2
94(72)
92(62)
96(67)
58
TolSiH3
PhMeSiH2
TolSiH3
TolH2Si-PHPh
PhMeHSi-PHPh
TolH2Si-PHCy
TolHSi(PHCy)2
PhMeHSi-PHCy
tBuH2Ge-PHPh
Ph2HGe-PHPh
complex mixture
with tBuH2Ge-PHCy
Ph2HGe-PHCy
Ph2Ge(PHCy)2
37
CyPH2
PhPH2
PhPH2
CyPH2
PhMeSiH2
tBuGeH3
Ph2GeH2
tBuGeH3
5
4
10
5
93(58)
92(86)
94(77)
61
33
50
CyPH2
Ph2GeH2
1.5
44
a Catalysis was performed in a sealed vessel in degassed benzene or
benzene-d6 solution at 90 °C with 5 mol % 1. b Characterization data for
new compounds can be found in the Supporting Information. c Reaction
time (days) is the length of time required to consume >95% of the phosphine
as monitored by 31P NMR spectroscopy. d Estimated yield of product(s)
measured by integration against an internal standard by 31P NMR
spectroscopy (isolated yield).
Figure 1. Molecular structure of 2 with thermal ellipsoids drawn at the
35% probability level. Methyl groups and hydrogen atoms, except H(1),
omitted for clarity. Selected bond lengths (Å) and angles (deg): Zr-P )
2.7254(6), P-C(21) ) 1.830(2), P-H(1) ) 1.33(2), Zr-N(3) ) 2.049(2),
Zr-N(1) ) 2.057(2), Zr-N(2) ) 2.072(2), Zr-N(4) ) 2.526(2); C(21)-
P-Zr ) 111.50(7), C(21)-P-H(1) ) 98.1(11), Zr-P-H(1) ) 96.1(11).
product silylphosphine was isolated by short-path distillation.
Likewise, CyPH2 readily underwent heterodehydrocoupling
with the TolSiH3 and PhMeSiH2 using complex 1 or 3 as a
catalyst.
Scheme 1. Proposed Catalytic Cycle for Heterodehydrocoupling of
Primary Phosphines with Silanes or Germanes
Reaction of PhPH2 with tBuGeH3 or Ph2GeH2 using 5 mol
% of complex 1 or 2 as a catalyst provided the secondary
germylphosphine with liberation of hydrogen (Table 1).
Reaction of CyPH2 with tBuGeH3 or Ph2GeH2 under analo-
gous conditions also resulted in catalytic heterodehydrocou-
pling. The formation of the germylphosphines is very clean
with respect to any byproducts and appears to be more facile
than the heterodehydrocoupling reactions with silanes. In a
direct comparison between Si and Ge, the catalytic hetero-
dehydrocoupling of PhPH2 and Ph2SiH2 proceeds but was
too sluggish to elaborate on here. In contrast, Ph2GeH2
reacted with PhPH2 under catalytic conditions, and while this
reaction was slow, Ph2HGe-PHPh was formed cleanly. This
difference in reactivity is significant. It may reflect both the
ca. 10% difference in E-H bond dissociation energies for
silicon and germanium, as well as the increased size of
germanium,9 which might allow for kinetic access to the
Ge-H bond. Such an analysis is based on the assumption
that the turnover-limiting step is P-E bond formation, and
studies are underway to test this working hypothesis.
Catalytic P-Ge bond formation via heterodehydrocoupling
appears not to have been previously reported. Additionally,
this appears to be the first instance of high-yielding, catalytic
heterodehydrocoupling involving primary phosphines and
silanes.5 Titanocene catalysts reported by Harrod and co-
workers efficiently heterodehydrocouple secondary phos-
phines and silanes, but at best, limited quantities of hetero-
dehydrocoupling products between CyPH2 and TolSiH3 were
observed.5 It was suggested that primary phosphines coor-
dinate too strongly to the titanium center and thus prohibit
heterodehydrocoupling. The sterically demanding trimeth-
ylsilyl-substituted triamidoamine ligand employed here may
prevent such coordination.
proposed to explain the observed reactivity (Scheme 1). In
these reactions, the respective phosphido complex, 2 or 3,
was the catalyst resting state, as observed by 1H and 31P NMR
spectroscopy (benzene-d6). Selective formation of a phos-
phido complex over silyl or germyl derivatives is not
unexpected given the potential stability of ligand-to-metal
π-bonding from a phosphido ligand.10 In the solid-state
structure of 2, (Figure 1) determined by a single-crystal X-ray
diffraction study, the phosphorus center is not planar (∑
(P) ) 305.7(1)°). Planarity at phosphorus is a feature
attributed to π-bonding despite theoretical studies on zir-
conocene complexes that have shown a pyramidal phospho-
rus is energetically favored.11 Though the Zr-P bond length
of 2 (2.7254(6) Å) is long compared to the range of
zirconocene complexes with terminal phosphido ligands
(2.488(1)-2.726(2) Å),10-12 the degree to which complex 2
engages in ligand-to-metal π-bonding is not clear. However,
it is well known that other metals supported by triamidoamine
ligands engage
(9) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. AdVanced
Inorganic Chemistry, 6th ed.; John Wiley and Sons: New York, 1999,
p. 259.
(10) Baker, R. T. Whitney, J. F. Wreford, S. S. Organometallics 1983, 2,
1049-1051.
(11) Urne˘zˇius, E.; Klippenstein, S. J.; Protasiewicz, J. D. Inorg. Chim. Acta
2000, 297, 181-189.
A catalytic cycle for this heterodehydrocoupling, based
partly on the known chemistry of (N3N)ZrPHPh,8 can be
(12) Hey-Hawkins, E. Chem. ReV. 1994, 94, 1661-1717.
6856 Inorganic Chemistry, Vol. 46, No. 17, 2007

COMMUNICATION
in multiple bonding.13 Thus, selective formation of phosphido
over silyl or germyl complexes may be due to factors other
than π-bonding.
dehydrocoupling of PhPH2 to (PhPH)2 under similar condi-
tions by 2 requires only 7 days.8 This observation implies
that the mechanism may be more complex than this working
hypothesis, possibly involving some degree of association
between Ph2GeH2 and 2 to prohibit competitive formation
of (PhPH)2.
In reactions with CyPH2, the products were susceptible
to heterodehydrocoupling with additional CyPH2. For in-
stance, reaction of TolSiH3 with CyPH2 gave predominately
TolH2Si-PHCy, but a second product, TolHSi(PHCy)2, was
also formed.5 Similarly, a second dehydrocoupling event to
form Ph2Ge(PHCy)2 was observed, and multiple heterode-
In summary, triamidoamine zirconium complexes are
effective catalysts for the heterodehydrocoupling of primary
phosphines with silanes and germanes. This catalysis pro-
vides hydrogen-rich silyl- and germylphosphines otherwise
accessible only by multistep stoichiometric syntheses.6
Efforts to uncover the root of the observed selectivity in this
catalysis and establish other novel bond-forming reactions
are underway.
t
hydrocoupling reactions of CyPH2 with BuGeH3 occurred.
Efficient separation of these products has yet to be uncovered,
and conditions that select exclusively for a single heterode-
hydrocoupling CyPH2 remain elusive. Reactions with CyPH2
were qualitatively faster than those with PhPH2, and only in
reactions with CyPH2 were multiple heterodehydrocoupling
events observed.
Another intriguing feature of the catalysis is the selectivity
for the zirconium phosphido complexes 2 or 3 to react
exclusively with Si-H or Ge-H bonds without competitive
formation of (RPH)2 (R ) Ph, Cy). For instance, the catalytic
heterodehydrocoupling of PhGeH2 and PhPH2 by 2 requires
10 days to proceed to completion. However, the catalytic
Acknowledgment. This work was supported by the
University of Vermont and the National Science Foundation
(Grant No. 0521237 to J.M.T.).
Supporting Information Available: Experimental details,
characterization data, and crystallographic data in cif format. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(13) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9-16.
IC7013144
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