Bis(diazasilaphosphetidines) and their metal complexes

Article abstract of DOI:10.1080/10426500490427213

The syntheses and solid-state structures of bis(diazasilaphosphetidines) of the type [Me₂Si(μ-N^tBu)₂P]₂NR, R = Ph, ⁱPr, ^tBu, of the P-chiral analogue [Me ₂Si(μ-N^tBu)(μ-N-2,6-ⁱPrPh)P] ₂(C₂H₄), and of some of their metal complexes are reported. The highly electron-rich, modular bis(phosphines) are easy to synthesize and may have applications in catalysis.

Full text of DOI:10.1080/10426500490427213

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Phosphorus, Sulfur, and Silicon and the Related
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BIS(DIAZASILAPHOSPHETIDINES) AND THEIR METAL
COMPLEXES
Graham R. Lief a , Ingo Schranz a & Lothar Stahl a
a University of North Dakota, Grand Forks , North Dakota, USA
Published online: 12 Aug 2010.
To cite this article: Graham R. Lief , Ingo Schranz & Lothar Stahl (2004) BIS(DIAZASILAPHOSPHETIDINES) AND THEIR METAL
COMPLEXES, Phosphorus, Sulfur, and Silicon and the Related Elements, 179:4-5, 813-816, DOI: 10.1080/10426500490427213
To link to this article: http://dx.doi.org/10.1080/10426500490427213
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Phosphorus, Sulfur, and Silicon, 179:813–816, 2004
ꢀC
Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490427213
BIS(DIAZASILAPHOSPHETIDINES) AND THEIR
METAL COMPLEXES
Graham R. Lief, Ingo Schranz, and Lothar Stahl
University of North Dakota, Grand Forks, North Dakota, USA
(Received September 4, 2003; accepted October 3, 2003)
The syntheses and solid-state structures of bis(diazasilaphos-
i
t
phetidines) of the type [Me2Si(µ-NtBu)2P]2NR, R = Ph, Pr, Bu, of
the P-chiral analogue [Me2Si(µ-NtBu)(µ-N-2,6-iPrPh)P]2(C2 H ), and
4
of some of their metal complexes are reported. The highly electron-rich,
modular bis(phosphines) are easy to synthesize and may have applica-
tions in catalysis.
Keywords:
Bis(diazasilaphosphetidines); bis(phosphines); diazadi-
phosphetidines; P,N-heterocycles; Si,N,P-heterocycles
Diazadiphosphetidines, ambidentate phosphorus-nitrogen molecules,
have been known for some time, but the comparatively low nucle-
ophilicity of their phosphorus atoms has made them poor phosphine
ligands, thereby limiting their role to building blocks for polymers1
and scaffolds for chelating amido ligands (Chart 1, 1 and 2).2,3 Re-
cent studies on tethered bis(diazasilaphosphetidines) (3), however, have
shown that the silicon-phosphorus analogues are much better phospho-
rus donors than diazadiphosphetidines.4 This electron-richness makes
these bis(diazasilaphosphetidines) good candidates for reactions requir-
ing electron-donating phosphines, e.g., homogenous hydrogenations
and polyolefin catalysis by late-transition metal complexes.5 Thus, for
example, [(Me2Si(µ-NtBu)2P)2C2H4Rh]BF4 reduces alkenes to alkanes
under mild conditions.
Enantioselective, homogeneous hydrogenations—key steps in the
synthesis of fine chemicals—are typically catalyzed by transition-
metal complexes bearing C2-symmetric ancillary ligands. For this
reason we developed a synthetic route for a C2-symmetric bis(dia-
zasilaphosphetidine) (Scheme 1) which yields a diphosphine with two
Address correspondence to Lothar Stahl, University of North Dakota, Department of
Chemistry, Box 9024, Grand Forks, ND 58202. E-mail: lstahl@chem.und.edu
813

814
G. R. Lief et al.
Cl
tBu
tBu
tBu
N
X
tBu
N
Cl
tBu
tBu
tBu
M
N
N
tBu
N
N
Si
P
P
Si
N
N
N
tBu
N
tBu
Cl
Cl
P
P
P
Ni
P
Ni
M
N
tBu
N
Ln
tBu
P(nBu)3
P(nBu)3
X = NR or C2H4
1
2
3
CHART 1
chiral phosphorus centers. Of the three possible products only the de-
sired S,S/R,R enantiomer pair was formed, as NMR-spectroscopic and
single-crystal x-ray diffraction studies showed. A clean separation of
the enantiomers, either in their pristine form or complexed to metals,
has thus far eluded us.
O
nBuLi
- 2 nBuH
PbCl2, - 78 o
- 2 LiCl
C
2
NH
NHtBu
N
Si
Pb
Si
N
tBu
O
tBu
Cl2P
N
2
Si
Pb
N
N
+
P
Si
Si
P
N
- 2 PbCl2
PCl2
N
tBu
N
tBu
SCHEME 1
The high cost of Cl2PC2H4PCl2 and the comparatively low yield make
the synthesis of bis(diazasilaphosphetidino)ethanediyl via the appro-
priate diazasilaplumbetidine (Scheme 1) inefficient. An attractive alter-
native for tethering two such heterocycles is by primary organoamines,
because of their low cost and ready availability. Concerns over the pre-
sumed lower electron-donating ability of tris(amino)phosphines, com-
pared to analogous alkylbis(amino)phosphines,6 proved unfounded, be-
cause IR-spectroscopic studies showed that tert-butylamine-tethered
bis(diazasilaphosphetidines) are even more electron-rich than alkyl-
tethered species. The versatility of constructing bis(phosphines) in this
manner is illustrated in Scheme 2, which shows that symmetrical and

Bis(diazasilaphosphetidines)
815
nBuLi
1.
Cl
tBu
N
-
nBuH
Cl
tBu
P
But
tBu
NH
tBu
N
Si
P
2.
LiHNPh
- LiCl
N
Si
N
Si
N
N
N
P
Si
P
Si
tBu
- LiCl
P
N
N
N
tBu
N
tBu
But
tBu
nBuLi
nBuH
1.
tBu
P
Ph2PCl
- LiCl
-
Si
N
N
2.
P
N
But
SCHEME 2
asymmetrical bis(phosphines) can be synthesized with relative ease.
Even amine-linkers of appreciable length, such as 1,6-diaminohexane,
may be used to synthesize tetrakis(diazasilaphosphetidino)phosphines
for the construction of one-dimensional coordination polymers or for the
synthesis of complexes with two remote catalytic sites.
To derivatize these organoaminobis(diazasilaphosphetidines) we
have, thus far, synthesized mainly nickel dibromide and molybde-
numtetracarbonyl derivatives, Scheme 3, but these ligands are equally
well suited for the coordination of zero-valent nickel and other late
transition metals.
tBu
P
But
tBu
P
But
Sb
Si
Si
N
N
N
Si
Si
N
N
N
NiBr2(CH3OC2H4)2O
- (CH3OC2H4)2O
Sb
N
N
N
N
But
tBu
But
tBu
Ni
Br
Br
tBu
P
tBu
P
Si
N
N
Si
N
N
cis-Mo(CO)4(pip)2
P
N
P
N
CO
Mo
But
- 2 pip
But
pip = piperidine
OC
CO
CO
SCHEME 3

816
G. R. Lief et al.
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