Structure and Reactivity of a Methyl Zinc Bis(iminophosphorano)methanide Chelate Complex

Article abstract of DOI:10.1021/om990415x

Reaction of dimethyl zinc with bis-{trimethylsilyliminodi(phenyl)phosphorano}methane, H₂C(Ph₂P=NSiMe₃)₂ (1), in toluene gave the alkyl zinc complex [ZnMe{HC(Ph₂P=NSiMe₃)₂-κ

Full text of DOI:10.1021/om990415x

Organometallics 1999, 18, 3775-3777
3775
Str u ctu r e a n d Rea ctivity of a Meth yl Zin c
Bis(im in op h osp h or a n o)m eth a n id e Ch ela te Com p lex
Aparna Kasani, Robert McDonald, and Ronald G. Cavell*
Department of Chemistry, University of Alberta, Edmonton, AB, Canada T6G 2G2
Received J une 1, 1999
Summary: Reaction of dimethyl zinc with bis-
{trimethylsilyliminodi(phenyl)phosphorano}methane,
H2C(Ph2PdNSiMe3)2 (1), in toluene gave the alkyl zinc
complex [ZnMe{HC(Ph2PdNSiMe3)2-κ2N,N′}] (2) via
elimination of methane. The crystal structure of the
complex confirms its monomeric nature and the biden-
tate coordination of the bis(iminophosphorano)methanide
ligand to the zinc. AdNCO (Ad ) adamantyl) reacted
smoothly with 2 via a nucleophilic addition forming a
new C-C bond in the novel tripodal alkyl zinc complex,
[ZnMe{HC{C(O)N(Ad)}(Ph2PdNSiMe3)2-κ3N,N′,N"}], 3.
The methine carbon atom resonances (δ 28.4 for 2 and
52.9 for 3) were observed as triplets due to the coupling
to two equivalent phosphorus atoms. The crystal struc-
ture of 3 shows a propeller type arrangement with the
three nitrogen atoms of the monoanionic tridentate
ligand bound to zinc.
that the less familiar bis(iminophosphorano)methanide
ligands (II) are isovalent-electronic to carbon-based
â-diimine ligands (I).
In this context we extended our study of bis(imino-
phosphorano)methane ligands16-19 to zinc, a post-
transition metal, because there is a fairly extensive
chemistry of monoanionic bis(iminophosphorano)methane
ligands with group 9 and 10 transition metals.20-28
Recently we described novel group 4 carbene complexes
with related ligand systems.17-19 Herein we report the
reaction of the prototypical ligand with ZnMe2 which
leads to a novel complex stabilized by bis(iminophos-
phorano)methanide chelation.
Organozinc compounds are widely used synthetic
reagents which offer valuable alternatives to the analo-
gous magnesium and lithium species in terms of both
reactivity and selectivity.1-6 Recently, zinc-based com-
plexes, particularly the aryloxide7-9 and â-diimine10,11
complexes, have been recognized as important catalysts
for copolymerization of carbon dioxide and epoxides to
polycarbonates. Other transition metal and main group
complexes of â-diimine ligand systems have also been
used for catalytic processes.10-15 Of relevance herein is
The complex [ZnMe{HC(Ph2PdNSiMe3)2-κ2N,N′}], 2,
was obtained as a colorless air-sensitive crystalline solid
in good yield upon the addition of 1 equiv of dimethyl
zinc to a toluene solution of H2C(Ph2PdNSiMe3)2, 1,29
(eq 1) under an argon atmosphere at room tempera-
ture.30 Methane is eliminated.
Complex 2 showed strong absorptions at 1259 and
1244 cm-1, which can be ascribed to the PdN stretch.
* To whom correspondence should be addressed. Telephone: 780-
492-5310. Fax: 780-492-8231. E-mail: ron.cavell@ualberta.ca.
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10.1021/om990415x CCC: $18.00 © 1999 American Chemical Society
Publication on Web 08/17/1999

3776 Organometallics, Vol. 18, No. 19, 1999
Communications
The 31P NMR spectrum of the final reaction mixture
showed that quantitative conversion of ligand 1 to
product 2 had occurred. The spectrum consisted of one
sharp singlet, indicating two equivalent phosphorus
atoms with a chemical shift of 26.2 ppm, shifted down-
field by 34.4 ppm vs the free ligand. The 13C{1H} APT
spectrum of 2 gave a negative triplet signal at 28.4 ppm
(1J PC ≈ 120.6 Hz) for the ligand backbone methanide
unit, coupled to two equivalent phosphorus nuclei.
The molecular structure of [ZnMe{HC(Ph2PdNSiMe3)2-
κ2N,N′}], 2, determined by X-ray crystallography31 is
illustrated (Figure 1). The ORTEP32 diagram shows the
atom-labeling scheme. Selected bond lengths and bond
angles are given in the caption. The core structure
consists of a six-membered metallacyclic ring with
Zn, N(1), P(1), C(1), P(2), and N(2) atoms adopting a
distorted boat conformation. Complex 2 is monomeric
in which the two phosphinimine units of the ligand
chelate to a monomethylated Zn to form a tricoordinated
distorted trigonal planar geometry {N(1)-Zn-N(2) )
99.4(1), N(1)-Zn-C(2) ) 128.9(2), C(2)-Zn-N(2) )
129.8(2)°}about the metal center. The sum of the angles
around zinc is 358.1(2)°; thus the zinc environment is
nearly planar. This tricoordinate environment for zinc
is rare, but not unknown;33-35 zinc is usually found in
a four-coordinate environment.
F igu r e 1. ORTEP32 view of [ZnMe{HC(Ph2PdNSiMe3)2-
κ2N,N′], 2, showing the atom-labeling scheme. Hydrogen
atoms are shown only on the methine and zinc methyl
centers. Only ipso phenyl carbon atoms are shown. The
remaining atoms are represented by Gaussian ellipsoids
at the 20% probability level. Selected interatomic distances
[Å] and angles [deg] are Zn-N(1) ) 2.083(3), Zn-N(2) )
2.042(3), Zn-C(2) ) 1.958(4), N(1)-P(1) ) 1.585(3),
P(1)-C(1) ) 1.728(4), P(2)-C(1) ) 1.739(4), P(2)-N(2) )
1.600(3), N(1)-Zn-N(2)
) 99.4(1), C(2)-Zn-N(1) )
128.9(2), C(2)-Zn-N(2) ) 129.8(2), P(1)-C(1)-P(2) )
120.1(2), N(1)-P(1)-C(1) ) 106.8(2), Zn‚‚‚C(1) ) 2.527(4).
toluene for 3 days, but did undergo addition reactions
with heteroallenes such as carbodiimides, isocyanates,
etc. Thus, adamantyl isocyanate reacted smoothly to
yield the novel four-coordinated derivative [ZnMe{HC-
{C(O)N(Ad)}(Ph2PdNSiMe3)2-κ3N,N′,N′′}] (3) (eq 2) con-
Complex 2 did not react with a nitrile (AdCN) or with
isonitriles (Ar′NC) even under reflux conditions in
(30) Preparation of [ZnMe{HC(Ph2PdNSiMe3)2-κ2N, N′], 2 All ex-
perimental manipulations were performed under rigorously anaerobic
conditions using Schlenk techniques or an argon-filled glovebox. To a
toluene (5 mL) solution of H2C(Ph2PdNSiMe3)2 (0.20 g, 0.36 mmol)
was added ZnMe2 (1.0 M solution in heptane, 0.36 mL, 0.36 mmol)
with stirring at room temperature. Immediate evolution of gas was
observed. The reaction mixture was stirred at room temperature for 1
day. Colorless crystals were obtained upon concentration of the solution
to half of the original volume and allowing the flask to stand at -15
°C for 3 days. The product was isolated by filtration and dried under
vacuum. Yield: 0.145 g, 63.5%. IR data (Nujol mull): 1589w, 1482m,
1436s, 1311w, 1259s, 1244s, 1160s, 1111s, 1069m, 1000m, 927s, 834s,
803s, 745s, 729s, 711s, 695s, 651s, 615m, 593s, 547s, 516s. 1H NMR
taining a tripodal ligand,36 by means of nucleophilic
addition of the methanide carbon to the adamantyl
carbon to form a new C-C bond. The reaction empha-
sizes the inertness of the methyl substituent on the zinc
which we surmise is due to steric protection of this unit
by the bulky ligand environment provided by the SiMe3
and Ad groups.33 Previous heteroallene insertion reac-
(C6D6): δ 7.65 (m, phenyl), 7.00 (m, phenyl), 1.92 (t, P-CH-P, 2J HP
)
4.5 Hz), 0.17 (s, CH3-Zn), 0.11 (s, CH3Si methyl). 13C {1H} NMR
(C6D6): Some phenyl resonances are second-order multiplets: δ 138.0
(m), 131.7 (m), 130.3 (s), 128.1 (m). Other resonances are: δ 28.4 (t,
1
3
P-CH-P, J PC ) 120.6 Hz), 3.6 (t, CH3Si, J PC ) 1.8 Hz), -9.3 (s,
CH3-Zn). 31P{1H} NMR (C6D6): δ 26.2(s). Anal. Calcd for C32H42N2P2-
Si2Zn: C, 60.22; H, 6.63; N, 4.39. Found: C, 59.99; H, 6.62; N, 4.37.
(31) Crystal data for [ZnMe{HC(Ph2PdNSiMe3)2-κ2N,N′], 2 : Tri-
clinic, P1h (No. 2), a ) 10.8871(3) Å, b ) 11.3994(4) Å, c ) 15.6589(6)
Å, R ) 81.555(3)°, â ) 87.067(2)°, γ ) 62.480(2)°, V ) 1704.5(1) Å3, Z
) 2. The structure was solved by direct methods and refined by full-
matrix least-squares procedures: R1 ) 0.0484 and 0.0513, (wR2 )
0.1142 and 0.1179) for 4149 reflections with Fo2 g 2σ(Fo2) and all data,
respectively.
(36) Preparation of [ZnMe{HC{C(O)N(Ad)}(Ph2PdNSiMe3)2-κ3N, N′,
N"}], 3 (also in the argon drybox). To a toluene (5 mL) solution of
[ZnMe{HC(Ph2PdNSiMe3)2-κ2N, N′], 2 (0.20 g, 0.31 mmol), was added
AdNCO (0.056 g, 0.31 mmol) and the mixture was stirred at room
temperature for a day. Concentration of the solution to half of the
original volume and allowing the flask to stand at -15 °C for 2 days
gave colorless crystals which were isolated by filtration and dried under
vacuum. Yield: 0.16 g, 62.6%. IR data (Nujol mull): 1611s, 1603s,
1587m, 1484w, 1438s, 1297s, 1247s, 1179s, 1166s, 1148s, 1125m,
1107s, 994w, 950w, 913m, 840s, 794w, 783w, 760m, 749m, 742m, 712s,
694s, 656m, 595m, 541m, 511s. 1H NMR (C6D6): δ 8.03 (m, phenyl),
7.17 (m, phenyl), 6.81 (m, phenyl), 6.59 (m, phenyl), 3.81 (t, P-CH-
(32) J ohnson, C. K. ORTEP, Report ORNL No. 5138; Oak Ridge Nat.
Labs: Oak Ridge, TN, 1976.
(33) Gorrell, I. B.; Looney, A.; Parkin, G. J . Am. Chem. Soc. 1990,
112, 4068-4069.
(34) Looney, A.; Han, R.; Gorrell, I. B.; Cornebise, M.; Yoon, K.;
Parkin, G.; Rheingold, A. L. Organometallics 1995, 14, 274-288.
(35) See for example: (a) Putzer, M. A.; Neumu¨ller, B.; Dehnicke,
K. Z. Anorg. Allg. Chem. 1997, 623, 539-544. (b) Bochmann, M.;
Bwembya, G. C.; Grinter, R.; Powell, A. K.; Webb, K. J .; Hursthouse,
M. B.; Malik, K. M. A.; Mazid, M. A. Inorg. Chem. 1994, 33, 2290-
2296. (c) Purdy, A. P.; George, C. F. Organometallics 1992, 11, 1955-
1959. (d) Ellison, J . J .; Ruhlandt-Senge, K.; Hope, H. H.; Power, P. P.
Inorg. Chem. 1995, 34, 49-54. (e) Chinn, M. S.; Chen, J . Inorg. Chem.
1995, 34, 6080-6084.
2
P, J HP ) 9.6 Hz), 2.33 (s, CH2-Ad), 2.21 (s, CH-Ad), 1.80 (dd, CH2-
Ad), 0.41 (s, CH3Si), 0.17 (s, CH3-Zn). 13C {1H} NMR (C6D6): Some
phenyl resonances are second-order multiplets: δ 132.6 (m), 132.3 (m),
131.9 (s), 131.0 (s), 127.9 (s). Other resonances are: δ 162.1 (t, CO,
1
2J PC ) 3.8 Hz), 56.1 (s, C-Ad), 52.9 (t, P-CH-P, J PC ) 44.6 Hz),
43.0 (s, CH2-Ad), 37.6 (s, CH2-Ad), 30.9 (s, CH-Ad), 4.4 (s, CH3Si),
-1.0 (s, CH3-Zn). 31P{1H} NMR (C6D6): δ 21.8 (s). Anal. Calcd for
C43H57N3OP2Si2Zn‚C7H8: C, 66.17; H, 7.22; N, 4.63. Found: C, 66.14;
H, 7.27; N, 4.66.

Communications
Organometallics, Vol. 18, No. 19, 1999 3777
tions37,38 of zinc alkyl amido complexes inserted into the
Zn-N bond yielding dimeric and oligomeric bridged
complexes;2 thus the reaction exhibited by 2 is unique.
The reaction of isocyanate with 2 is also different from
the reactions of isocyanates with â-ketoimines and
â-dicarbonyls; in these cases the methine hydrogen atom
was replaced and an amine was formed.39-41
Complex 3 was isolated as a colorless crystalline solid
sensitive to air and moisture. The Infrared spectrum
showed strong absorptions at 1611, 1603 cm-1 and at
1297 cm-1 due to the CdO and PdN stretching vibra-
tions. Only a single peak was observed in the phospho-
rus NMR spectrum, indicating that the phosphorus
atoms are equivalent. The 13C{1H} APT spectrum for
the CH of the P-C-P frame consisted of a negative
triplet (1J PC ≈ 44.6 Hz) at 52.9 ppm, (downfield shift of
24.5 ppm with respect to 2). The monomeric molecular
structureof[ZnMe{HC{C(O)N(Ad)}(Ph2PdNSiMe3)2-κ3N,-
N′,N′′}], 3,42 confirmed by X-ray crystallography is
illustrated in an ORTEP32 plot (Figure 2). The metal is
subtended by a methyl group and three nitrogens, one
from the isocyanate adduct and the other two are the
previously chelated phosphinimine centers. The basic
framework consists of three six-membered rings fused
at two opposite apexes to form a propeller. The non-
bonding distance across the chelate ring in 3 (i.e., Zn to
C(1)), 3.009(2) Å, is longer than this separation in
complex 2 (2.527(4) Å); thus the addition of the AdNCO
opens the structure. There is no interaction between the
zinc and the carbonyl group of the AdNCO, which in
any case faces away from the metal. In 3, the zinc center
is located in a trigonally distorted tetrahedral geometry,
a shape similar to that observed previously for the η3-
bis(pyrazolyl)hydroborato complexes of zinc.34,43 The
newly added nitrogen, N(3), has a slightly shorter bond
to Zn than the chelated imine bonds, Zn-N(1) and Zn-
N(2), indicating that the negative charge is more local-
ized on N(3). The range of observed Zn-N distances is
within that observed for Zn-amide complexes.44,45 The
zinc methyl distances in 2 and 3 are in the range
observed for other terminal zinc alkyl complexes.46
The bond distances within the ligand framework in
2 and 3 are considerably altered in comparison with the
related values in free bis(iminophosphorane) ligands;22,47
the PdN bond distances are slightly elongated and the
F igu r e 2. ORTEP32 view of [ZnMe{HC{C(O)N(Ad)}(Ph2-
PdNSiMe3)2-κ3N,N′,N"}], 3, showing the atom-labeling
scheme. For clarity all hydrogen atoms (except for those
on the methine center and the zinc methyl center) and all
phenyl group carbon atoms (except the ipso carbon) have
been removed. Remaining atoms are represented by Gauss-
ian ellipsoids at the 20% probability level. Selected inter-
atomic distances [Å] and angles [deg] are Zn-N(1) )
2.132(2), Zn-N(2)
) 2.191(2), Zn-N(3) ) 2.050(2),
Zn-C(3) ) 1.998(2), N(1)-P(1) ) 1.576(2), P(1)-C(1) )
1.827(2), P(2)-C(1) ) 1.817(2), P(2)-N(2) ) 1.573(2), N(1)-
Zn-N(2) ) 99.94(7), N(1)-Zn-N(3) ) 96.42(7), N(2)-Zn-
N(3) ) 94.53(7), P(1)-C(1)-P(2) ) 119.9(1), N(1)-P(1)-
C(1) ) 110.9(1).
P-C-P bond angles (120.1(2)° in 2 and 119.9(1)° in 3)
are expanded compared to the corresponding values in,
for example, CH3CH{Ph2PdN(Tol)}2 (112.39(19°)22 and
H2C{Cy2PdNSiMe3}2 (117.41(12)°).47 The endocyclic
P-C bond distances are shorter in complex 2 than
comparable bonds in the free ligands, although they are
essentially unchanged in complex 3. These factors
suggest that there is a delocalization of π electron
density within the six-membered ZnN2P2C ring in 2
which is not applicable in 3.
The alkyl zinc complex 2 of the bis(iminophosphora-
no)methanide ligand is the first example of a group 12
complex of the bis(iminophosphorano)methane ligand
system. The complex contains a rare example of a three-
coordinated zinc center. Nucleophilic addition to the
carbon center of an isocyanate gave a novel tripodal
four-coordinated zinc complex. Reactivity studies are
presently being pursued.
(37) Lappert, M. F.; Power, P. P.; Sanger, A. R.; Srivastava, R. C.,
Metal and Metalloid Amides; Ellis Horwood, New York, 1980.
(38) Noltes, J . G. Rec. Trav. Chim. 1965, 84, 126.
(39) Howells, P. N.; Kenney, J . W.; Nelson, J . H.; Henry, R. A. Inorg.
Chem. 1976, 15, 124-129.
(40) Eckberg, R. P.; Henry, R. A.; Cary, L. W.; Nelson, J . H. Inorg.
Chem. 1977, 16, 2977-2979.
Ack n ow led gm en t. We thank the Natural Sciences
and Engineering Research Council of Canada, NOVA
Chemicals Ltd., and the University of Alberta for
financial support.
(41) Collman, J . P. Angew. Chem., Int. Ed. Engl. 1965, 4, 132-138.
(42) Crystal data for [ZnMe{HC{C(O)N(Ad)}(Ph2PdNSiMe3)2-
κ3N,N′,N"}], 3: triclinic, P1h (No. 2), a ) 10.2782(5) Å, b ) 14.0288(8)
Å, c ) 17.532(1) Å, R ) 88.134(1)°, â ) 75.317(1)°, γ ) 85.654(1)°, V )
2438.1(2) Å3, Z ) 2. The structure was solved by direct methods and
refined by full-matrix least-squares procedures: R1 ) 0.0382 and
Su p p or tin g In for m a tion Ava ila ble: This material is
available free of charge via the Internet at http://pubs.acs.org.
2
0.0541, (wR2 ) 0.0919 and 0.0974) for 7103 reflections with Fo
g
2σ(Fo2) and all data, respectively.
(43) Gorrell, I. B.; Looney, A.; Parkin, G. J . Chem. Soc., Chem.
Commun. 1990, 220-222.
(44) Malik, M. A.; O’Brien, P.; Motevalli, M.; J ones, A. C. Inorg.
Chem. 1997, 36, 5076-5081.
OM990415X
(45) Olmstead, M. M.; Grigsby, W. J .; Chacon, D. R.; Hascall, T.;
Power, P. P. Inorg. Chem. Acta 1996, 251, 273-284.
(46) Almenningen, A.; Helgaker, T. U.; Haaland, A.; Samdal, S. Acta
Chem. Scand. 1982, A36, 156-159.
(47) Manuscript in preparation. Includes the X-ray structure of CH2-
{Cy2PdNSiMe3}2: Kamalesh Babu, R. P.; McDonald, R.; Cavell, R. G.
Report RGC 9802; University of Alberta Structure Determination
Laboratory.