Synthesis and structural characterization of zinc complexes of the imido-amido phosphate anions OP[(NHR)3-x(NR)]x- (R = Me, t-Bu; x = 1-3) and EP[(NH-t-Bu)2(N-t-Bu)]- (E = S, NSiMe3)

Article abstract of DOI:10.1139/v05-183

The reaction of OP(NH-t-Bu)₃ with 1 equiv. of ZnMe₂ generates the dimeric eight-membered ring {MeZn[(μ-NH-t-Bu)(μ-N-t-Bu)P(NH- t-Bu)(μ-O)]}₂ (5) and the cubane {[MeZn]₃[OP(N-t-Bu) ₃][OP(NH-t-Bu)₃]} (6), which contains the first known trisimidophosphate trianion. A related complex {Zn[ZnMe]₂[OP(N-t-Bu) (NH-t-Bu)₂][OP(N-t-Bu)₃]} (7) is obtained by the reaction of OP(NH-t-Bu)₃ with ZnMe₂ in a 2:3 molar ratio. The treatment of OP(NHMe)₃ with 1 equiv. of ZnMe₂ produces the oxide-templated cluster {Zn₄(μ₄-O)[OP(NMe)(NHMe) ₂]₄[OP(NMe)₂(NHMe)]}₂ (8). Each half of this centrosymmetric dimer contains a tetrahedral arrangement of four 4-coordinate Zn²⁺ ions surrounding the central μ₄- O^2- anion. The reaction of SP(NH-t-Bu)₃ with ZnMe ₂ in a 1:1 molar ratio generates the dimer {MeZn(μ-S)(μ-N-t-Bu) P(NH-t-Bu)₂}₂ (10), which has a ladder-type structure. When a 2:1 molar ratio of the same reagents is employed, the bis(N,S)-chelated complex {Zn[(μ-S)(μ-N-t-Bu)P(NH-t-Bu)₂]₂} (11) is obtained. The monomeric N,N′-chelated complex {MeZn[(μ-N-t-Bu)(μ- NSiMe₃)P(NH-t-Bu)₂]} (12) results from the reaction of Me₃SiNP(NH-t-Bu)₃ with 1 equiv. of dimethylzinc. All new compounds have been characterized by multinuclear (¹H, ¹³C, and ³¹P) NMR spectroscopy and, in the case of 5, 6, 7, 8, and 10, by X-ray structural determinations.

Full text of DOI:10.1139/v05-183

1768
Synthesis and structural characterization of zinc
complexes of the imido–amido phosphate anions
OP[(NHR)3–x(NR)]x– (R = Me, t-Bu; x = 1–3) and
EP[(NH-t-Bu)2(N-t-Bu)]– (E = S, NSiMe3)
Andrea F. Armstrong, Tristram Chivers, Mark Krahn, and Masood Parvez
Abstract: The reaction of OP(NH-t-Bu)3 with 1 equiv. of ZnMe2 generates the dimeric eight-membered ring
{MeZn[(µ-NH-t-Bu)(µ-N-t-Bu)P(NH-t-Bu)(µ-O)]}2 (5) and the cubane {[MeZn]3[OP(N-t-Bu)3][OP(NH-t-Bu)3]} (6),
which contains the first known trisimidophosphate trianion. A related complex {Zn[ZnMe]2[OP(N-t-Bu)(NH-t-
Bu)2][OP(N-t-Bu)3]}(7) is obtained by the reaction of OP(NH-t-Bu)3 with ZnMe2 in a 2:3 molar ratio. The treatment of
OP(NHMe)3 with 1 equiv. of ZnMe2 produces the oxide-templated cluster {Zn4(µ4-O)[OP(NMe)(NHMe)2]4[OP(NMe)2-
(NHMe)]}2 (8). Each half of this centrosymmetric dimer contains a tetrahedral arrangement of four 4-coordinate Zn2+
ions surrounding the central µ4-O2– anion. The reaction of SP(NH-t-Bu)3 with ZnMe2 in a 1:1 molar ratio generates the
dimer {MeZn(µ-S)(µ-N-t-Bu)P(NH-t-Bu)2}2 (10), which has a ladder-type structure. When a 2:1 molar ratio of the same
reagents is employed, the bis(N,S)-chelated complex {Zn[(µ-S)(µ-N-t-Bu)P(NH-t-Bu)2]2} (11) is obtained. The
monomeric N,N ′-chelated complex {MeZn[(µ-N-t-Bu)(µ-NSiMe3)P(NH-t-Bu)2]} (12) results from the reaction of
Me3SiNP(NH-t-Bu)3 with 1 equiv. of dimethylzinc. All new compounds have been characterized by multinuclear (1H,
13C, and 31P) NMR spectroscopy and, in the case of 5, 6, 7, 8, and 10, by X-ray structural determinations.
Key words: zinc, phosphate, imido ligands, sulfur.
Résumé : La réaction du OP(NH-t-Bu)3 avec un équivalent de ZnMe2 conduit à la formation du cycle dimère à huit
chaînons {MeZn[(µ-NH-t-Bu)(µ-N-t-Bu)P(NH-t-Bu)(µ-O)]}2 (5) et du cubane {[MeZn]3[OP(N-t-Bu)3][OP(NH-t-Bu)3]}
(6) qui contient le premier trisimidophosphate connu. Le complexe apparenté {Zn[ZnMe]2[OP(N-t-Bu)(NH-t-
Bu)2][OP(N-t-Bu)3]} (7) est obtenu lors de la réaction du OP(NH-t-Bu)3 avec du ZnMe2 dans un rapport de 2 : 3. Le
traitement du OP(NHMe)3 avec un équivalent de ZnMe2 conduit à la formation de l’agrégat avec gabarit d’oxyde
{Zn4(µ4-O)[OP(NMe)(NMe)2]4[OP(NMe)2(NHMe)]}2 (8). Chacune des moitiés de ce dimère centrosymétrique com-
prend un arrangement tétraédrique de quatre ions Zn2+ tétracoordinés qui entourent l’anion µ4-O2– central. La réaction
du SP(NH-t-Bu)3 avec du ZnMe2 dans un rapport molaire de 1 : 1 génère la formation du dimère {MeZn(µ-S)(µ-N-t-
Bu)P(NH-t-Bu)2}2 (10) dont la structure est en échelle. Quand on utilize un rapport 2 : 1 des même réactifs, on obtient
le complexe bis-N,S-chélaté {Zn[(µ-S)(µ-N-t-Bu)P(µ-NH-t-Bu)2]2} (11). Le complexe N,N ′-chélaté monomère
{MeZn[(µ-N-t-Bu)(µ-NSiMe3)P(NH-t-Bu)2]} (12) résulte de la réaction du Me3SiNP(NH-t-Bu)3 avec un équivalent de
diméthylzinc. Tous les nouveaux composés ont été caractérisés par spectroscopie RMN (1H, 13C et 31P) et dans les cas
des composés 5, 6, 7, 8 et 10, par diffraction des rayons X.
Mots clés : zinc, phosphate, ligands imido, soufre. Armstrong et al. 1778
Introduction
ligands generates a series of polyimido anions that are
isoelectronic with phosphate. The introduction of an alkyl or
aryl substituent on nitrogen is expected to result in
polyimido anions whose metal complexes will exhibit sig-
nificantly different structures and chemical properties com-
pared with those of [PE4]3– (E = O, NH). In addition, one or
more of the oxo substituents in a polyimido phosphate can
be replaced by a heavier chalcogen, such as sulfur, to create
The preparation and structural characterization of imido
analogues of common phosphorus oxoanions is an active
area of main group chemistry (1, 2). The imido group
[NH]2– is formally isoelectronic with the oxo [O]2–
substituent;2 partial or complete replacement of the oxygen
atoms in an oxoanion such as orthophosphate [PO4]3– by NH
Received 26 April 2005. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 13 December 2005.
A.F. Armstrong, T. Chivers,1 M. Krahn, and M. Parvez. Department of Chemistry, University of Calgary, Calgary,
AB T2N 1N4, Canada.
1Corresponding author (e-mail: chivers@ucalgary.ca).
2The original definition of “isoelectronic” (isosteric) compounds restricts the term to species having the same number of atoms and
the same number of electrons (I. Langmuir. J. Am. Chem. Soc. 41, 1543 (1919)). Thus, according to this definition, N3– is
isoelectronic with O2–. However, nitrides are compositionally different to oxides as a result of the different charges on the anions.
Can. J. Chem. 83: 1768–1778 (2005)
doi: 10.1139/V05-183
© 2005 NRC Canada

Armstrong et al.
1769
ligands with different coordinating properties as a result of
the presence of both hard (N) and soft (S) binding sites.
In recent years, we have thoroughly investigated the reac-
tivities of the triamidophosphates OP(NH-t-Bu)3 (1a) (3, 4),
SP(NHR)3 (2, R = alkyl, aryl) (4, 5), and Me3SiNP(NH-t-
Bu)3 (3) (3, 6) toward alkyllithium reagents. The mono- and
di-lithium salts {Li[(µ-N-t-Bu)(µ-O)P(NH-t-Bu)2]}3·THF (4)
and the double cubane {Li2[OP(NH-t-Bu)(N-t-Bu)2]}2·4THF,
isoelectronic with [H2PO4]– and [HPO4]2–, respectively, are
readily obtained by treatment of 1a with n-BuLi. However,
complete deprotonation of 1a to give the trianion [OP(N-t-
ane, and diethyl ether were dried over Na/benzophenone,
distilled, and stored over molecular sieves prior to use.
Dimethylzinc (1.0 and 2.0 mol/L solutions in toluene) was
used as received from Aldrich. Me3SiNP(NH-t-Bu)3 (3),
OP(NHR)3 (R = Me, t-Bu) (4), and SP(NH-t-Bu)3 (5) were
prepared according to the literature procedures.
Instrumentation
7
1H, Li, 13C, and 31P NMR spectra were collected on a
Bruker DRX-400 spectrometer with chemical shifts reported
relative to Me4Si in CDCl3 (1H and 13C), LiCl in D2O (7Li),
and 85% H3PO4 in D2O (31P). All spectra were collected at
22 °C, with the exception of compound 10 (spectra recorded
at –30 °C). Infrared spectra were recorded as Nujol mulls on
KBr plates using a Nicolet Nexus 470 FT IR spectrometer in
the range 4000–400 cm–1. Mass spectra were recorded on a
Bruker Esquire 3000 ESI ion trap mass spectrometer. Ele-
mental analyses were provided by the Analytical Services
Laboratory, Department of Chemistry, University of Calgary.
Bu)3]3– could not be achieved (3, 4). The mono- and di-
x–
anions [OP(N-t-Bu)x(NH-t-Bu)3–x
]
(x = 1 or 2) are also
produced from the reactions of 1a with AlMe3 or LiAlH4
(7).
Similar reactivity was observed for the thiophosphates
SP(NHR)3 (2a (R = t-Bu), 2b (R = i-Pr)) (4, 5). The mono-
and di-lithium salts of 2b ({Li[(µ-N-i-Pr)(µ-S)P(NH-i-
Pr)2]}2·2THF) and {[Li(TMEDA)]2[SP(NH-i-Pr)(N-i-Pr)2]}2
have been isolated and characterized, as has a mixed
monolithium–dilithium derivative of 2a; attempts to generate
[SP(N-i-Pr)3]3– resulted in sulfur extrusion. Trilithiation can
be achieved, however, by replacement of the alkyl substitu-
ents by more electron-withdrawing para-tolyl groups; in this
case, the trisimidothiophosphate {Li3[SP(Np-tol)3]} is readily
obtained (4).
Preparation of {MeZn[(␮-NH-t-Bu)(␮-N-t-Bu)P(NH-t-
Bu)(␮-O)]}2 (5) and {[MeZn]3[OP(N-t-Bu)3][OP(NH-t-
Bu)3]} (6)
A solution of ZnMe2 (0.70 mL, 2.0 mol/L, 1.40 mmol) in
toluene was added to a slurry of OP(NH-t-Bu)3 (0.366 g,
1.39 mmol) in toluene (20 mL) at 22 °C, resulting in a clear
solution after 10 min. The reaction mixture was heated at
60 °C for 4 h; the solvent was then removed under vacuum
to give a white powder (0.417 g). 31P{1H} NMR (C6D6) δ:
46.8, 28.6, 24.3 (minor), 13.2 (minor), 11.3, 10.2, 9.3 (br),
8.1 (s).
Recrystallization of the product (72 mg) from toluene
yielded colourless crystals of 5 (35 mg, 0.051 mmol, 21%
based on ZnMe2). 13C{1H} NMR (solid state, 12 kHz) δ:
53.03 (s, NCMe3), 52.28 (s, µ-HNCMe3), 49.79 (s,
HNCMe3), 34.52 (s, NCMe3), 32.05 (s, µ-HNCMe3), 31.44
(s, HNCMe3), –11.63 (s, MeZn). 31P{1H} NMR (C6D6) δ:
9.3 (br), 8.1 (s). 31P{1H} NMR (solid state, 5 kHz) δ: 7.4 (s).
Anal. calcd. for C38H64N6O2P2Zn2: C 45.73, H 9.45, N 12.31;
found: C 45.53, H 9.68, N 12.36.
In sharp contrast to the somewhat limited reactivities of the
chalcogen systems 1a and
2 toward n-BuLi, both
symmetrical and unsymmetrical tetraimidophosphates,
{Li3[P(NPh)4]} (8) and {Li3[P(NR)3(NSiMe3)]} (3) (R = t-
Bu, Cy), respectively, are readily prepared by the reaction of
the corresponding iminophosphorane (RNH)3PNR with 3 equiv.
of n-butyllithium.
Zinc phosphates are the second-largest family of the well-
known metal phosphate open-framework materials and have
applications as both catalysts and molecular sieves. These
materials are generally prepared under hydro- or solvo-
thermal conditions; the three-dimensional structures of the
products are highly dependent upon reaction conditions such
as temperature and time, and the presence and shape of a
templating agent (9–11). Consequently, it is of interest to ex-
plore the possibility of preparing a series of zinc imido-
phosphates. While the steric bulk of the imido groups is
expected to hinder aggregation resulting in the formation of
much smaller oligomers than the extended networks that are
characteristic of metal-phosphate complexes (12), it remains
to be seen whether these systems will exhibit similar de-
pendencies on reaction conditions as do the zinc phosphates.
In addition, it is germane to examine the modes of coordina-
tion of these multidentate ligands for comparison with their
behaviour in the lithium derivatives (3–6). In an attempt to
shed light upon these and other points, we have investigated
the reactions of the triamidophosphates OP(NHR)3 (R = Me, t-
Bu), SP(NH-t-Bu)3, and Me3SiNP(NH-t-Bu)3 towards
dimethylzinc.
Recrystallization of the product (51 mg) from Et2O
yielded colourless crystals of 6 (14 mg, 0.018 mmol, 32%
1
based on ZnMe2). H NMR (C6D6) δ: 2.30 (br, 3H, NH),
1.38 (s, 9H, NCMe3), 1.33 (s, 27H, NHCMe3), 1.09 (s, 18H,
NCMe3), –0.12 (s, 9H, MeZn+). 31P{1H} NMR (C6D6) δ:
46.8, 10.2. Anal. calcd. for C27H66N6O2P2Zn2: C 42.39, H
8.70, N 10.99; found: C 42.02, H 8.93, N 11.21.
Preparation of {Zn[MeZn]2[OP(N-t-Bu)(NH-t-
Bu)2][OP(N-t-Bu)3]} (7)
A solution of ZnMe2 (5.34 mL, 1.0 mol/L, 5.34 mmol) in
toluene was added dropwise to a solution of OP(NH-t-Bu)3
(0.937 g, 3.56 mmol) in toluene (25 mL) at 22 °C. The tolu-
ene solution was refluxed at 113 °C for 18 h yielding a clear,
colourless solution. The volume was reduced to 10 mL and
after 1 day at 22 °C, colourless crystals of 7 had formed
Experimental
1
(0.601 g, 0.802 mmol, 45%). IR (cm–1): 3279 (ν(N-H)). H
NMR (C6D6) δ: 2.05 (br s, NH), 1.75–1.18 (numerous reso-
nances, NCMe3), 0.29 (s, ZnCH3). 31P{1H} NMR (C6D6) δ:
22.0 (s), 14.6 (s), 13.1 (s) (1:1:1), and additional minor reso-
Reagents and general procedures
All experiments were carried out under an argon atmo-
sphere using standard Schlenk techniques. Toluene, n-hex-
© 2005 NRC Canada

1770
Can. J. Chem. Vol. 83, 2005
nances; solid state (10 kHz) δ: 22.0 (s), 13.5 (s). MS (ESI+):
(20 mL) at 22 °C, resulting in an opaque yellow mixture.
After 3 h, the solvent was removed under vacuum to give 12
as a yellow paste (0.400 g, 0.966 mmol, 91%). Washing
with organic solvents did not improve the physical appear-
ance of this highly soluble paste, which was shown to be
549 (M+ – 199).
Preparation of {Zn4(␮4-O)[OP(NMe)(NHMe)2]4[OP-
(NMe)2(NHMe)]}2 (8)
1
pure 12 on the basis of spectroscopic and analytical data. H
A solution of ZnMe2 (1.18 mL, 1.0 mol/L, 1.18 mmol) in
toluene was added dropwise to a solution of OP(NHMe)3
(0.162 g, 1.18 mmol) in toluene (25 mL) at 22 °C. The tolu-
ene solution was heated at reflux for 24 h. The volume of
the solution was reduced to one-half and the concentrate was
placed in the freezer. After 7 days at –15 °C, colourless
crystals of 8·C7H8 were recovered (0.144 g, 0.0718 mmol,
NMR (C6D6) δ: 1.75 (br, NH), 1.22 (s, 27H, CMe3), 0.27 (s,
9H, SiMe3), –0.24 (s, 3H, MeZn). 13C{1H} NMR (C6D6) δ:
51.14 (d, CMe3, 2J(13C-31P) = 8.9 Hz), 50.41 (d, CMe3,
2J(13C-31P) = 11.9 Hz), 34.06 (d, CMe3, 3J(13C-31P) =
3
34.2 Hz), 32.42 (d, CMe3, J(13C-31P) = 15.5 Hz), 4.61 (d,
3
SiMe3, J(13C-31P) = 12.5 Hz), –15.0 (s, ZnMe). 31P{1H}
1
49% based on ZnMe2). IR (cm–1): 3323 (ν(N-H)). H NMR
NMR (C6D6) δ: 9.1 (s). Anal. calcd. for C16H41N4PSiZn: C
46.42, H 9.98, N 13.53; found: C 46.50, H 10.05, N 13.86.
(C6D6) δ: 2.25 (s, NHMe), 2.22 (s, NHMe), 2.20 (s, NHMe),
2.16 (s, NHMe) (1:1:1:1), 1.36 (br s, NMe). 31P{1H} NMR
(C6D6) δ: 37.9 (s), 28.2 (s) (relative intensities ~1:3), and ad-
ditional minor resonances; solid state (13 kHz) δ: 38.7 (s),
27.6 (s). Anal. calcd. for C37H116N30O12P10Zn8: C 22.15, H
5.83, N 20.94; found: C 22.02, H 6.05, N 19.96.
X-ray analyses
Colourless crystals of 5, 6, 7, 8·C7H8, and 10 were coated
with Paratone 8277 oil and mounted on a glass fibre. All
measurements were made on a Nonius Kappa CCD
diffractometer using graphite-monochromated molybdenum–
Kα radiation. Crystallographic data are summarized in Ta-
ble 1. The structures were solved by direct methods (13) and
refined by full-matrix least-squares methods with SHELXL-
97 (14). Hydrogen atoms were included at geometrically
idealized positions and were not refined; the non-hydrogen
atoms were refined anisotropically. Thermal ellipsoid plots
were created using Diamond version 2.1 (15). Additional
data are available in the Supporting information.3
Preparation of [MeZn(␮-S)(␮-N-t-Bu)P(NH-t-Bu)2]2 (10)
A solution of ZnMe2 (0.83 mL, 2.0 mol/L, 1.66 mmol) in
toluene was added slowly to a slurry of SP(NH-t-Bu)3
(0.461 g, 1.65 mmol) in toluene (20 mL) at 22 °C. The clear
solution was stirred for 18 h; the solvent was then removed
under vacuum to give 10 as a white powder (0.468 g,
1
0.652 mmol, 79%). H NMR (C6D6) δ: 2.15 (br, NH), 1.48
4
(s, 9H, N), 1.31 (d, J(1H-31P) = 6.8 Hz, 18H, NHCMe3), –0.1
(s, 3H, MeZn+). 13C{1H} NMR (C6D6) δ: 53.90 (d, CMe3,
2J(13C-31P) = 44.4 Hz), 51.63 (d, CMe3, 2J(13C-31P) =
3
19.3 Hz), 33.40 (d, CMe3, J(13C-31P) = 27.7 Hz), 30.41 (d,
Results and discussion
3
CMe3, J(13C-31P) = 136.5 Hz). 31P{1H} NMR (C6D6) δ:
39.3 (s). Anal. calcd. for C26H62N6P2S2Zn2: C 43.68, H 9.03,
N 11.76; found: C 44.33, H 9.28, N 11.87.
Reactions of OP(NHR)3 with ZnMe2 — Formation and
structures of {MeZn[(␮-NH-t-Bu)(␮-N-t-Bu)P(NH-t-
Bu)O]}2 (5), {[MeZn]3[OP(N-t-Bu)3][OP(NH-t-Bu)3]} (6),
and {Zn[ZnMe]2[OP(N-t-Bu)(NH-t-Bu)2][OP(N-t-Bu)3]} (7)
Initial attempts to conduct a thorough investigation of the
reactivity of ZnMe2 towards OP(NHR)3 (1a (R = t-Bu), 1b
(R = Me), 1c (R = Ad)) were confounded by the subtle de-
pendence of these reactions upon both temperature and time.
A mixture of products was observed by 31P NMR spectros-
copy in all cases. Both the number and relative intensities of
the resonances observed were strongly influenced by minor
changes in the reaction conditions so that reproducible re-
sults were difficult to obtain, except for the reaction of 1a
with 1 equiv. of dimethylzinc at 60 °C. The solid-state 31P
NMR spectrum of the white powder produced in this reac-
tion contains a single broad signal centred at 7 ppm. In solu-
tion at 22 °C, eight 31P NMR resonances of various
intensities and linewidths were observed, suggesting the
presence of multiple products. A variable-temperature NMR
experiment showed that the linewidths, relative intensities,
and indeed the number of resonances present are dependent
upon temperature, indicating that this system is highly dy-
namic in solution and suggesting that different modes of ag-
Preparation of {Zn[(␮-S)(␮-N-t-Bu)P(NH-t-Bu)2]2} (11)
A solution of ZnMe2 (0.58 mL, 2.0 mol/L, 1.16 mmol) in
toluene was added slowly to a slurry of SP(NH-t-Bu)3
(0.648 g, 2.32 mmol) in toluene (20 mL) at 22°C. The re-
sulting clear solution was stirred for 18 h; the solvent was
then removed under vacuum to give 11 as an analytically
1
pure white powder (0.710 g, 1.14 mmol, 98%). H NMR
(C6D6) δ: 2.12 (br, 2H, NH), 1.44 (s, 9H), 1.32 (s, 18H,
2
CMe3). 13C{1H} NMR (C6D6) δ: 54.06 (d, CMe3, J(13C-
2
31P) = 43.5 Hz), 51.82 (d, CMe3, J(13C-31P) = 9.9 Hz),
3
34.18 (d, CMe3, J(13C-31P) = 38.7 Hz), 31.67 (d, CMe3,
3J(13C-31P) = 17.1 Hz). 31P{1H} NMR (C6D6) δ: 42.0 (s).
Anal. calcd. for C24H58N6P2S2Zn: C 46.33, H 9.40, N 13.51;
found: C 45.30, H 10.64, N 13.48.
Preparation of {MeZn[(␮-N-t-Bu)(␮-NSiMe3)P(NH-t-
Bu)2]} (12)
A solution of ZnMe2 (0.53 mL, 2.0 mol/L, 1.06 mmol) in
toluene was added slowly to a pale yellow solution of
Me3SiNP(NH-t-Bu)3 (0.357 g, 1.07 mmol) in hexane
3 Supplementary data for this article are available on the Web site or may be purchased from the Depository of Unpublished Data, Document
Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 4056. For more information on obtaining mate-
rial refer to http://cisti-icist.nrc-cnrc.gc.ca/irm/unpub_e.shtml. CCDC 269284–269287 contain the crystallographic data for this manuscript.
These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2005 NRC Canada

Armstrong et al.
1771
Table 1. Crystallographic data.
5
6
7
8
10
Formula
C26H64N6P2O2Zn2
C27H66N6P2O2Zn2
C26H62N6O2P2Zn3
C23H62N15O6 P5Zn4
C13H32N3PSZn
fw (g)
Space group
a (Å)
b (Å)
c (Å)
685.51
P1
764.97
Pna21
22.936(5)
10.445(2)
16.213(3)
90
90
90
3884.2
4
748.87
Pca21
19.286(7)
17.059(11)
22.530(11)
90
90
90
7412(7)
8
1049.20
C2/c
17.5081(2)
23.6571(3)
21.4354(4)
90
101.3377(5)
90
8705.1(2)
4
358.82
P21/c
11.854(3)
9.678(2)
17.108(6)
90
107.818(15)
90
1868.5(9)
2
9.764(2)
9.854(2)
11.230(2)
64.54(3)
71.01(3)
72.64(3)
906.4(3)
1
α (°)
β (°)
γ (°)
V (Å3)
Z
T (K)
173(2)
0.71073
1.256
173(2)
0.71073
1.121
173(2)
0.71073
1.342
173(2)
0.71073
1.601
173(2)
0.71073
1.275
λ (Å)
dcalcd (g cm–3)
µ (mm–1)
F(000)
Ra
1.441
368
0.035
0.093
1.340
1400
0.0355
0.0799
2.042
3168
0.1198
0.3503
2.410
4336
0.040
0.107
1.505
768
0.0411
0.0763
b
Rw
aR = [Σ||Fo| – |Fc||]/[Σ |Fo|] for reflections with I > 2.00σ(I).
2
2
bRw = {[Σw(Fo – Fc2)2]/[Σw(Fo )2]}1/2 for all reflections.
gregation can occur for these products, even in the
noncoordinating solvent d8-toluene.
Fig. 1. Thermal ellipsoid plot of 5 (30% probability ellipsoids).
Only α-carbon atoms of the t-Bu groups are shown.
Recrystallization of the white powder from toluene re-
sulted in the isolation of colourless crystals, which were
characterized by X-ray crystallography and multinuclear
NMR spectroscopy; crystal data are compiled in Table 1. An
X-ray structure, depicted in Fig. 1, showed the crystals to
consist of the monoanion [OP(N-t-Bu)(NH-t-Bu)2]– with a
methylzinc counterion. The complex {MeZn[(µ-NH-t-Bu)(µ-
N-t-Bu)P(NH-t-Bu)(µ-O)]}2 (5) exists as a centrosymmetric
dimer. Each of the methylzinc cations is chelated by a t-
BuNH and a t-BuN group of one monoanion, with a Zn—O
bond serving to both link the zinc atom to the second
monoanion and to complete the tetrahedral coordination
sphere of the Zn atom. The second t-BuNH group on each
phosphorus centre is not coordinated to either of the
methylzinc cations.
C26
O1
N3
N1
Zn2
P1
N2
N4
N5
P2
Zn1
O2
N6
C25
Selected bond lengths and bond angles for 5 are summa-
rized in Table 2. Three different P—N bond lengths and two
distinct Zn—N distances are observed: the Zn(1)—N(1) bond
length (1.980(9) Å) is substantially shorter than the Zn(1)—
N(2) distance (2.430(8) Å), reflecting the greater strength of
the zinc–imido linkage. Similarly, the P(1)—N(1) bond
distance (1.590(8) Å) is considerably shorter than the P(1)—
N(2) single-bond distance of 1.705(8) Å. The fact that N(3)
is not coordinated to an electropositive zinc centre results in
a shorter, stronger P—N bond (P(1)—N(3) 1.627(9) Å) than
that observed for the coordinated N(2) atom. The Zn—O
distances in 5 are slightly longer than those typically ob-
served in zinc phosphates, with an average value of 2.001(7) Å,
cf., mean values of 1.936(4) Å in the histidine complex
[Zn(HPO4)·(C6H9N3O2)] (9) and 1.933(2) Å in the amino-
benzene-templated system [Zn(HPO3)2·C6N2H10] (11). As
expected, the bond angle at the sp2 nitrogen atom (pP(1)-
N(1)-Zn(1), 102.5(5)°) is larger than the corresponding
angle involving the sp3 amido nitrogen atom (pP(1)-N(2)-
Zn(1), 83.1(3)°), though both angles markedly deviate from
ideal values, presumably owing to steric repulsions among
the three tert-butyl groups attached to the nitrogen atoms.
The structure of 5 is a sharp contrast to the trimeric struc-
ture adopted by the lithium salt {Li[(µ-N-t-Bu)(µ-O)P(NH-t-
Bu)2]}3·THF (4) (4), which contains the same monoanion.
The Li+ cations in 4 are coordinated only by the oxo- and N-
t-Bu ligands, while the NH-t-Bu groups are exocyclic.
Whereas 5 is centrosymmetric, the trimer 4 displays C1 sym-
metry, due in part to the presence of a molecule of THF co-
ordinated to one Li+ cation. Some of these structural
differences can be attributed to the high polarity of Li-E
(E = N or O) units and their consequent propensity for ag-
gregation to form ladder-type motifs.
The solid-state 31P and 13C NMR data for 5 were consis-
tent with the X-ray structure; a major 31P resonance is ob-
served at 7.4 ppm, and three distinct 13C signals for the
© 2005 NRC Canada

1772
Can. J. Chem. Vol. 83, 2005
Table 2. Selected bond lengths (Å) and bond
angles (°) for 5.
Fig. 2. Thermal ellipsoid plot of 6 (30% probability ellipsoids).
Only α-carbon atoms of the t-Bu groups are shown.
O1
Bond lengths (Å)
P(1)—O(1)
P(1)—N(2)
Zn(1)—O(1)
Zn(1)—N(1)
Zn(1)—C(25)
P(1)—N(1)
P(1)—N(3)
Zn(1)—O(2)
Zn(1)—N(2)
1.495(7)
1.705(8)
2.000(7)
1.980(9)
1.970(10)
1.590(8)
1.627(9)
2.001(7)
2.430(8)
N2
P1
Zn3
N1
Zn2
N3
Zn1
O2
Bond angles (°)
P(1)-N(1)-Zn(1)
P(1)-N(2)-Zn(1)
P(1)-O(1)-Zn(2)
O(1)-Zn(2)-C(26)
P(1)-O(1)-Zn(2)
O(1)-P(1)-N(1)
N(1)-Zn(1)-O(2)
N(3)-P(1)-O(1)
N(2)-P(1)-N(3)
N5
N4
P2
N6
102.5(5)
83.1(3)
152.2(4)
109.6(4)
154.2(4)
122.5(5)
107.7(3)
106.8(4)
110.7(4)
(6), which is comprised of the trianion [OP(N-t-Bu)3]3– and
three MeZn+ counterions, with a neutral molecule of 1a co-
ordinated to two of the zinc centres. The formation of this
previously unobserved trianion was somewhat unexpected
given the lack of success encountered in attempts to gener-
ate [OP(N-t-Bu)3]3– using organolithium reagents (4). In ad-
dition, the presence of unreacted OP(NH-t-Bu)3 concomitant
with the formation of this trianion is rather surprising; the
generation of a mixture of mono- and di-anions would seem
more probable.
N
Ht-Bu
t-BuHN
t-BuN
P
NHt-Bu
O
O
N
Ht-Bu
Li
P
In the solid state, 6 exists as a distorted PN3Zn3O cube,
with the phosphorus and nitrogen atoms of the [OP(N-t-
Bu)3]3– trianion contributing four of the vertices, while the
remaining positions are occupied by the three zinc cations
and the oxygen atom O(2) of the neutral OP(NH-t-Bu)3 mol-
ecule. While O(2) is coordinated to two of the methylzinc
cations, the =P(NH-t-Bu)3 fragment is pendant from the
cube. Selected bond lengths and bond angles for 6 are given
in Table 3. The oxo ligand of the trianion is exo to the clus-
ter, with a P(1)—O(1) bond distance of 1.475(2) Å, cf.,
1.474(3) Å in 1a (4). In contrast, the P(2)—O(2) bond
length is significantly longer (1.519(2) Å) because of coordi-
nation of this oxygen atom to two zinc atoms. The increase
in this P=O distance has little effect on the P—N bond
lengths in the neutral fragment; the average P(2)—N
distance is 1.631(3) Å, cf., 1.637(3) Å in 1a (4). The mean
P—N bond length in the trianion is significantly longer
(1.689(3) Å), since the nitrogen atoms in this moiety are
four-coordinate.
Two of the zinc centres are four-coordinate, with two
Zn—N bonds, one Zn—O linkage, and a methyl substituent,
while the third zinc cation exhibits only a weak Zn—O con-
tact (2.648(2) Å) and is thus considered three-coordinate.
The zinc–oxygen distances for the two four-coordinate zinc
atoms are Zn(1)—O(2) = 2.333(2) Å and Zn(2)—O(2) =
2.314(2) Å. These Zn—O distances are substantially longer
than the mean values of 1.980(4) Å found in zinc-
di(oxo)cyclodiphosph(V)azane systems (16), or the distances
reported for the polymeric di(tert-butyl)phosphates {Zn[O2P-
(O-t-Bu)2]2[H2N(CH2)6NH2]}n and {Zn[O2P(O-t-Bu)2]2}n
(range: 1.914(8)–1.929(6) Å) (17). The mean Zn—N dis-
Li
Li
THF
O
Nt-Bu
t-BuN
P
t-Bu
Ht-Bu
N
N
4
inequivalent CMe3 groups occur at 34.52, 32.05, and
31.44 ppm. In C6D6 solution, however, the 31P NMR spec-
trum consists of a sharp singlet at 8.1 ppm and a broader
resonance at 9.3 ppm, possibly owing to an equilibrium be-
tween the dimer 5 and the corresponding monomer
{[MeZn][(N-t-Bu)P(O)(NH-t-Bu)2]}. A variable-temperature
NMR experiment showed that, at low temperature (–50 °C),
the 8.1 ppm species is predominant, while the intensity of
the resonance at 9.3 ppm increases at higher temperatures,
consistent with the proposed monomer–dimer equilibrium.
The apparently facile dissociation of 5 into the correspond-
ing monomer is somewhat surprising in light of its relatively
strong Zn—O linkages (vide supra). Interestingly, the solid-
state 31P NMR spectrum of 5 also displays a minor reso-
nance at 9.8 ppm, which may be attributable to the presence
of a small amount of the monomer.
When the product of the reaction of OP(NH-t-Bu)3 with
1 equiv. of ZnMe2 at 60 °C was recrystallized from diethyl
ether rather than toluene, colourless crystals of a different
product were obtained. An X-ray structure (Fig. 2) identified
this compound as {[MeZn]3[OP(N-t-Bu)3][OP(NH-t-Bu)3]}
© 2005 NRC Canada

Armstrong et al.
Table 3. Selected bond lengths (Å) and bond
1773
zinc centres, all of which are four-coordinate: the Zn2+
dication is also coordinated to nitrogen donors, while the
other zinc atoms are also bound to two nitrogen atoms and a
methyl substituent.
angles (°) for 6.
Bond lengths (Å)
P(1)—O(1)
P(1)—N(2)
P(2)—O(2)
P(2)—N(5)
Zn(1)—N(1)
Zn(2)—N(2)
Zn(1)—O(2)
P(1)—N(1)
P(1)—N(3)
P(2)—N(4)
P(2)—N(6)
Zn(1)—N(3)
Zn(2)—N(3)
Zn(2)—O(2)
1.476(2)
1.696(2)
1.519(2)
1.627(3)
2.091(2)
2.079(3)
2.333(2)
1.686(2)
1.684(3)
1.642(3)
1.625(3)
2.046(2)
2.074(2)
2.314(2)
O
t-BuN
P
Me
Zn
Nt-Bu
t-Bu
Zn
Me
N
O
P
Zn
N
t-Bu
t-BuHN
t-BuHN
7
Bond angles (°)
N(1)-P(1)-N(2)
N(2)-P(1)-N(3)
N(1)-Zn(1)-O(2)
N(2)-Zn(2)-N(3)
N(3)-Zn(2)-O(2)
Zn(1)-O(2)-Zn(2)
N(1)-P(1)-N(3)
N(1)-Zn(1)-N(3)
N(3)-Zn(1)-O(2)
N(2)-Zn(2)-O(2)
N(1)-Zn(3)-N(2)
98.1(1)
99.1(1)
The solid-state 31P NMR spectrum of 7 consists of two
singlets at 22.0 and 13.5 ppm, consistent with the X-ray
structure. In C6D6 solution, the 31P NMR spectrum exhibits
three major resonances at 22.0, 14.6, and 13.1 ppm, suggest-
ing that more than one mode of aggregation occurs in solu-
tion; consistently, the solution 1H NMR spectrum of 7
contains numerous resonances in the N-t-Bu region.
89.62(9)
76.54(9)
86.29(9)
86.26(7)
99.4(1)
76.82(9)
86.46(9)
89.11(9)
77.52(9)
The contrasting structures of 5, 6, and 7 suggest that there
are two different pathways possible for the reaction of
dimethylzinc with OP(NH-t-Bu)3. Complex 6 is clearly a
precursor of 7; in a separate experiment, it was shown by 31
P
NMR spectroscopy that crystalline 6 can, in fact, be con-
verted to 7 by thermal elimination of methane under reduced
pressure (Scheme 1). At the same time, 5 is clearly not a
precursor of 6, despite the fact that the first step in the for-
mation of both 5 and 6 is likely the monodeprotonation of
OP(NH-t-Bu)3. In the case of 6, the second step of the reac-
tion results in the double deprotonation of one of the lig-
ands.
The different coordination modes of the two ligands
within both 6 and 7 are also noteworthy. The oxo unit of one
ligand (the trianion) remains exo to the cubane, while the
other oxygen atom plays an integral role in cluster forma-
tion, as it is coordinated to either two or three zinc centres in
6 and 7, respectively. Additionally, two distinct modes of co-
ordination for the [OP(N-t-Bu)(NH-t-Bu)2]– monoanion are
observed in these complexes, with N,O chelation displayed
in 7, whereas N,N′ chelation prevails in 5; similar N,N′ coor-
dination also occurs for the trianionic ligands in 6 and 7, but
in those two instances the oxo substituent remains non-
coordinated.
tance for the three-coordinate zinc cation Zn(3) is 2.040(2) Å,
cf., 2.073(2) Å for the four-coordinate zinc centres. The
mean pN-P-N bond angle is 98.9(1)° while the pN-Zn-N
and pN-Zn-O bond angles range from 76.54(9)° to 89.62(9)°.
A
31P NMR spectrum of 6 in C6D6 solution displayed two
sharp singlets at 46.8 and 10.2 ppm, which are assigned to
the [OP(N-t-Bu)3]3– trianion and the neutral OP(NH-t-Bu)3
ligand, respectively. Three resonances are observed in the 1H
NMR spectrum with relative intensities of 3:1:2, attributed
to the three NH-t-Bu groups of the coordinated molecule of
1a (27H) and the inequivalent N-t-Bu ligands of the trianion
(9H and 18H), while a single broad resonance at –0.12 ppm
is assigned to the methylzinc cations. These NMR data are
consistent with the solid-state structure of 6.
When the reaction of 1a with dimethylzinc was carried
out in a 2:3 molar ratio in boiling toluene, the 31P NMR
spectrum of the resulting white powder indicated the forma-
tion of a mixture of products. However, recrystallization
from toluene produced a single compound identified as
{Zn[ZnMe]2[OP(N-t-Bu)(NH)2][OP(N-t-Bu)3]} (7) by X-ray
crystallography. Although the structure could not be satisfac-
torily refined (R1 = 0.12) because of poor diffraction of the
crystals and disorder of the tert-butyl substituents, the atom
connectivities of 7 were established. Complex 7 is closely
related to 6 in that its primary structural feature is a
PN3Zn3O cube; however, in place of the neutral OP(NH-t-
Bu)3 ligand of 6, complex 7 contains a monoanion [OP(N-t-
Bu)(NH-t-Bu)2]– that is N,O chelated to a Zn2+ dication. The
oxo substituent of this monoanion is coordinated to all three
Formation and X-ray structure of {Zn4(␮4-O)-
[OP(NMe)(NHMe)2]4[OP(NMe)2(NHMe)]}2 (8)
Following the successful generation of the trisimidophos-
phate trianion [OP(N-t-Bu)3]3– utilizing dimethylzinc, simi-
lar reactions with tris(methylamido)phosphate OP(NHMe)3
(1b) were investigated to determine the effect of the replace-
ment of the bulky tert-butyl groups of 1a with the much
smaller NMe units on the size of the zinc imidophosphate
clusters formed. The reaction of dimethylzinc with 1b in a
© 2005 NRC Canada

1774
Can. J. Chem. Vol. 83, 2005
Scheme 1. Thermal conversion of 6 to 7.
O
O
N
P
t-Bu
t-BuN
P
Me
Zn
Me
Zn
Nt-Bu
Nt-Bu
t-Bu
t-Bu
N
Me Zn
Me
Zn
N
-CH4
O
P
Zn
Zn
Me
O
P
Nt-Bu
t-BuHN
t-BuHN
t-BuHN
NHt-Bu
t-BuHN
7
6
Fig. 3. Thermal ellipsoid plot of 8 (30% probability ellipsoids). Hydrogen atoms of methyl groups are omitted.
1:1 ratio in boiling toluene led to the isolation of colourless
Fig. 4. Structural framework of 8. All methyl groups and
noncoordinated NHMe groups are omitted for clarity.
crystals of the oxide-templated complex {Zn4(µ4-O)-
[OP(NMe)(NHMe)2]4[OP(NMe)2(NHMe)]}2 (8) in 49% yield.
An X-ray structure of 8 revealed that this complex is a
centrosymmetric dimer, which crystallizes with a molecule
of toluene in its lattice. A thermal ellipsoid plot is shown in
Fig. 3, while the framework of the cluster is pictorially rep-
resented in Fig. 4. Each monomeric unit consists of four
Zn2+ ions, four [OP(NMe)(NHMe)2]– monoanions, one
[OP(NMe)2(NHMe)]2– dianion, and one oxide ligand; in
each half of the cluster there is a tetrahedral core of four 4-
coordinate Zn2+ ions that surround a central µ4-O2– anion.
The four monoanions bridge four edges of the Zn4 tetrahe-
dron. The two halves of the molecule are joined together by
the two [OP(NMe)2(NHMe)]2– dianions, while the NHMe
P
P
N
O
O
N
N
Zn
N
O
Zn
Zn
Zn
N
O
P
N
P
P
O
O
P
O
O
N
O
N
P
O
P
Zn
Zn
Zn
N
Zn
N
N
P
O
O
N
P
© 2005 NRC Canada

Armstrong et al.
1775
Table 4. Selected bond lengths (Å) and bond
angles (°) for 8.
group of each dianion does not participate in cluster bond-
ing. Three of the four Zn2+ ions (Zn(1), Zn(2), and Zn(4))
interact with the two dianions and thus participate in linking
together the two halves of the dimer. As a result of these
linkages, there are numerous six-, eight-, ten-, and twelve-
membered rings in the structure. The Zn and O atoms reside
near the centre of the cluster, while the methyl groups of the
phosphate anions point away from the central core.
Bond lengths (Å)
Zn(1)—N(4)
Zn(1)—N(1)
Zn(1)—O(3)
Zn(1)—O(6)
Zn(2)—O(4)
Zn(2)—O(2)a
Zn(2)—O(6)
Zn(2)—N(5)
Zn(3)—N(13)
Zn(3)—O(6)
Zn(3)—N(10)
Zn(3)—O(1)
Zn(4)—O(6)
Zn(4)—N(7)
Zn(4)—O(5)
Zn(4)—N(5)a
P(1)—O(1)
P(1)—N(1)
P(1)—N(2)
P(1)—N(3)
P(2)—O(2)
P(2)—N(4)
P(2)—N(6)
P(2)—N(5)
P(3)—O(3)
1.971(3)
1.999(3)
2.005(3)
2.026(2)
1.969(3)
1.964(2)
1.957(2)
2.045(2)
1.958(3)
1.989(2)
1.992(3)
2.055(2)
1.974(2)
1.986(3)
2.045(2)
2.079(2)
1.515(2)
1.605(3)
1.633(3)
1.650(3)
1.532(2)
1.602(3)
1.646(3)
1.667(3)
1.498(3)
1.607(3)
1.652(3)
1.660(3)
1.522(2)
1.598(3)
1.639(3)
1.649(4)
1.589(4)
1.515(2)
1.640(3)
1.671(3)
The X-ray structure described in the preceding section is
expected to give rise to five resonances in the 31P NMR
spectrum of 8. However, a solution 31P NMR spectrum in d6-
benzene revealed two dominant resonances at 37.9 and
28.2 ppm in an approximately 1:4 ratio, while the solid-state
spectrum exhibited only two singlets centred at 38.7 and
27.6 ppm. These observations are tentatively attributed to the
similar chemical environments experienced by the four crys-
tallographically inequivalent [OP(NMe)(NHMe)2]– mono-
anions, which result in the appearance of only one resonance
for those four phosphorus atoms, along with a second reso-
nance attributed to the [OP(NMe)2(NHMe)2]2– dianion. The
1
solution H NMR spectrum of 8 exhibits four singlets of
equal intensities at 2.25, 2.22, 2.20, and 2.16 ppm, assigned
to the four different environments of the NHMe groups,
while a single broad resonance centred at 1.36 ppm is ob-
served for the indistinguishable NMe substituents. While no
1
NH resonance could be detected in the H NMR spectrum,
the NHMe fragments were clearly identified by a sharp N-H
stretch (3323 cm–1) in the IR spectrum of 8.
The formation of the much larger cluster 8, as compared
with complexes 5, 6, and 7, is a direct consequence of the
decrease in steric bulk of the NR groups, which allows for
more extensive aggregation. Roesky and co-workers (18, 19)
have reported the synthesis of a zinc complex of tert-
butylphosphonic acid, [Zn2(THF)2(EtZn)6Zn4(µ4-O)(t-BuPO3)8]
(9), with a structure similar to that of 8: complex 9 contains
a central Zn4(µ4-O) core, with the tert-butylphosphonate lig-
ands radiating outwards from the centre of the dodeca-
nuclear cluster. Selected bond lengths and bond angles for 8
are summarized in Table 4. The phosphorus–µ2-O bond
lengths range from 1.498(3) to 1.532(2) Å (cf., 1.499(5)–
1.527(5) Å in 9). The zinc–µ4-O distance is also similar to
those of 9 (1.957(2)–2.026(2) Å in 8; 1.948(4)–2.073(4) Å
in 9); however, the Zn—µ2-O distances are significantly lon-
ger in 8 than those in 9 (1.964(2)–2.055(1) Å vs. 1.891(5)–
1.990(5) Å, respectively).
The origin of the µ4-oxygen atom of 8 remains uncertain.
It has been suggested that the presence of oxide in 9 results
from the dehydration of tert-butylphosphonic acid induced
by diethylzinc (19). However, this explanation is clearly not
applicable to the reaction of ZnMe2 with OP(NHMe)3. Pos-
sible sources of the oxide ligand in the current case include
(a) P=O bond cleavage during the course of the reaction,
(b) the contamination of the reagent 1b by water, or (c) the
presence of “adventitious” water during the recrystallization
process, as suggested for related systems (17, 20). As 31P
NMR studies of the reaction mixtures gave no evidence for
P=O bond cleavage, and the IR spectrum of 1b showed that
it was anhydrous, the most probable source of the oxide unit
is the introduction of moisture during the recrystallization
process.
P(3)—N(7)
P(3)—N(8)
P(3)—N(9)
P(4)—O(4)
P(4)—N(10)
P(4)—N(11)
P(4)—N(12)
P(5)—N(13)
P(5)—O(5)
P(5)—N(14)
P(5)—N(15)
Bond angles (°)
N(4)-Zn(1)-N(1)
N(13)-P(5)-N(15)
N(4)-Zn(1)-O(3)
N(14)-P(5)-N(15)
N(14)-P(5)-N(15)
N(1)-Zn(1)-O(3)
P(1)-O(1)-Zn(3)
N(4)-Zn(1)-O(6)
P(2)-O(2)-Zn(2)a
N(1)-Zn(1)-O(6)
P(3)-O(3)-Zn(1)
O(3)-Zn(1)-O(6)
P(4)-O(4)-Zn(2)
O(6)-Zn(2)-O(2)a
P(5)-O(5)-Zn(4)
O(6)-Zn(2)-O(4)
Zn(2)-O(6)-Zn(4)
O(2)a-Zn(2)-O(4)
Zn(2)-O(6)-Zn(3)
124.56(11)
117.63(16)
106.27(10)
100.88(16)
100.88(16)
98.83(11)
121.67(14)
109.48(10)
133.13(12)
108.6(1)
130.67(16)
107.51(9)
125.79(14)
111.28(8)
126.97(13)
111.61(9)
109.04(10)
105.71(9)
104.22(9)
© 2005 NRC Canada

1776
Can. J. Chem. Vol. 83, 2005
Table 4 (concluded).
Fig. 5. Thermal ellipsoid plot of 10 (30% probability ellipsoids).
Only hydrogen atoms bonded to nitrogen atoms are shown.
Bond angles (°)
O(6)-Zn(2)-N(5)
Zn(4)-O(6)-Zn(3)
O(2)a-Zn(2)-N(5)
Zn(2)-O(6)-Zn(1)
O(4)-Zn(2)-N(5)
O(1)-P(1)-N(2)
N(1)-P(1)-N(2)
O(1)-P(1)-N(3)
P(4)-N(10)-Zn(3)
N(1)-P(1)-N(3)
N(2)-P(1)-N(3)
O(2)-P(2)-N(4)
O(2)-P(2)-N(6)
N(4)-P(2)-N(6)
O(2)-P(2)-N(5)
N(4)-P(2)-N(5)
N(6)-P(2)-N(5)
O(3)-P(3)-N(7)
O(3)-P(3)-N(8)
Zn(4)-O(6)-Zn(1)
Zn(3)-O(6)-Zn(1)
P(1)-N(1)-Zn(1)
N(13)-Zn(3)-O(6)
N(13)-Zn(3)-O(6)
N(13)-Zn(3)-N(10)
O(6)-Zn(3)-N(10)
N(13)-Zn(3)-O(1)
O(6)-Zn(3)-O(1)
P(2)-N(4)-Zn(1)
N(10)-Zn(3)-O(1)
P(2)-N(5)-Zn(2)
N(10)-Zn(3)-Zn(2)
O(1)-Zn(3)-Zn(2)
P(2)-N(5)-Zn(4)a
O(6)-Zn(4)-N(7)
Zn(2)-N(5)-Zn(4)a
O(6)-Zn(4)-O(5)
N(7)-Zn(4)-O(5)
O(6)-Zn(4)-N(5)a
N(7)-Zn(4)-N(5)a
P(3)-N(7)-Zn(4)
O(5)-Zn(4)-N(5)a
O(1)-P(1)-N(1)
N(7)-P(3)-N(8)
O(3)-P(3)-N(9)
N(7)-P(3)-N(9)
N(8)-P(3)-N(9)
O(4)-P(4)-N(10)
O(4)-P(4)-N(11)
N(10)-P(4)-N(11)
O(4)-P(4)-N(12)
N(10)-P(4)-N(12)
N(11)-P(4)-N(12)
O(5)-P(5)-N(13)
O(5)-P(5)-N(14)
N(13)-P(5)-N(14)
O(5)-P(5)-N(15)
118.42(9)
110.93(10)
103.71(9)
110.67(9)
105.07(10)
110.45(15)
107.12(16)
104.80(15)
116.75(15)
110.10(16)
108.71(16)
108.48(12)
114.66(13)
109.53(14)
105.23(12)
114.35(13)
104.66(13)
110.36(15)
107.33(16)
108.18(9)
113.71(10)
113.64(16)
117.01(10)
117.01(10)
112.50(11)
111.18(10)
105.55(11)
109.56(9)
116.69(15)
99.34(10)
105.20(13)
75.03(8)
106.81(7)
114.87(13)
120.77(10)
103.58(10)
101.62(8)
101.59(10)
114.13(9)
114.42(10)
120.41(16)
99.70(9)
115.53(16)
114.25(16)
114.75(15)
108.98(15)
101.00(16)
110.00(14)
107.17(15)
116.08(16)
112.26(15)
108.23(16)
103.01(17)
109.46(14)
115.83(14)
108.36(16)
104.78(14)
N3
S1
Zn1*
N2
N1*
P1*
P1
N1
N2*
N3*
S1*
Zn1
Preparation and characterization of [MeZn(␮-S)(␮-N-t-
Bu)P(NH-t-Bu)2]2 (10) and {Zn[(␮-S)(␮-N-t-Bu)P(NH-t-
Bu)2]2} (11)
The reaction of SP(NH-t-Bu)3 with
1 equiv. of
dimethylzinc produces {MeZn(µ-S)(µ-N-t-Bu)P(NH-t-Bu)2}2
(10) in 78% yield. An X-ray structure (Fig. 5) revealed that
in the solid state, 10 exists as a centrosymmetric dimer in
which each ligand is N,S chelated to a MeZn+ cation, with
Zn—S bonds linking the two halves together into a step-
shaped ladder motif. Each zinc atom is thus four-coordinate,
with two Zn—S linkages, one Zn—C bond, and a Zn-N-t-Bu
unit. Selected bond lengths and bond angles for 10 are given
in Table 5. As expected, the mean P—N distances involving
the pendant NH-t-Bu groups (1.650(2) Å) are longer than
the P-N(t-Bu) linkage (1.592(2) Å). The substantial differ-
ence between the Zn(1)—N(1) (2.007(2) Å) and Zn(1)—
S(1) (2.5849(9) Å) bond lengths, combined with the tetrahe-
dral geometries of the phosphorus and zinc atoms, gives the
four-membered PNSZn rings a distorted diamondoid shape.
The Zn2S2 ring is closer to square-shaped, with bond angles
of 97.10(3)° and 82.90(3)° at the zinc and sulfur centres, re-
spectively. Two distinct Zn—S distances are observed with
the shorter bond (2.4627(9) Å) linking the two monomeric
units and contributing to the distortion of the ring.
The dimeric laddering arrangement exhibited by 10 has
been observed for other complexes of imidophosphate
monoanions. The lithium derivatives {Li[(µ-N-t-Bu)(µ-
NSiMe3)P(NH-t-Bu)2]}2 (6) and {Li[(µ-N-i-Pr)(µ-S)P(NH-i-
Pr)2]}2·2THF (5) both display this connectivity. The latter
thiophosphate complex and 13 both exist in the trans confor-
mation to minimize steric repulsions between the bulky tert-
butyl substituents. The different mode of coordination of the
heteroleptic imidophosphate ligand to zinc in 10 compared
with that in 5 may be attributed, in part, to the greater affin-
ity of zinc for the softer sulfur centre, resulting in N,S
chelation, while N,N′ coordination is observed for the O-
containing ligand in 5. This, in turn, results in significantly
different modes of oligomerization for these two dimers. It
should be noted that the first transition-metal complexes of
the monoanion [SP(N-t-Bu)(NH-t-Bu)2]– have been reported
recently (21); interestingly, both N,S and N,N′ chelation were
observed in a single Ni(II) complex.
a–x + 1/2, –y + 1/2, –z.
© 2005 NRC Canada

Armstrong et al.
Table 5. Selected bond lengths (Å) and bond
1777
NHt-Bu
S
t-BuHN
t-BuHN
S
angles (°) for 10.
P
Zn
P
Bond lengths (Å)
P(1)—N(1)
P(1)—N(3)
Zn(1)—S(1)
P(1)—N(2)
P(1)—S(1)
N
t-Bu
N
t-Bu
NHt-Bu
1.592(2)
1.651(2)
2.4627(9)
1.648(2)
2.0501(11)
1.966(3)
11
Preparation and characterization of {MeZn[(␮-N-t-Bu)-
(␮-NSiMe3)P(NH-t-Bu)2]} (12)
Zn(1)—C(1)
The reaction of (t-BuNH)3PNSiMe3 with 1 equiv. of
dimethylzinc generates {MeZn[(µ-N-t-Bu)(µ-NSiMe3)P(NH-
t-Bu)2]} (12) as a yellow oil, which has been characterized
by multinuclear NMR spectroscopy and CHN analysis. The
1H NMR spectrum of 12 exhibits only three resonances with
relative intensities of 9:3:1 assigned to the t-Bu groups, the
SiMe3 substituent, and the MeZn+ cation, respectively. Al-
though the signals from the µ-N-t-Bu and NH-t-Bu groups
Bond angles (°)
S(1)-Zn(1)-S(1)a
S(1)-P(1)-N(1)
S(1)-P(1)-N(3)
N(2)-P(1)-N(3)
N(1)-Zn(1)-C(1)
S(1)-Zn(1)-N(1)
Zn(1)-N(1)-P(1)
N(1)-P(1)-N(2)
S(1)-Zn(1)-C(1)
N(1)-Zn(1)-S(1)
97.10(3)
101.66(9)
108.51(9)
100.42(12)
121.18(10)
82.90(3)
106.22(12)
110.49(13)
121.18(10)
75.19(7)
1
are not resolved in the H NMR spectrum, the 13C NMR
spectrum shows two distinct sets of t-Bu resonances in an
approximately 1:2 ratio. A singlet is observed at 9.1 ppm in
the 31P NMR spectrum. Thus, the NMR data indicate a
N,N′-chelated structure for 12.
aSymmetry transformations used to generate
equivalent atoms: –x + 1, –y + 1, –z.
t-Bu
N
NHt-Bu
NHt-Bu
The 31P NMR spectrum of 10 in C6D6 at 22 °C exhibits
resonances at 41.1 and 39.6 ppm in an approximately 1:3 ra-
tio, rather than the expected single peak; multiple resonances
P
Me
Zn
N
SiMe3
1
are observed in the H NMR spectrum. Variable-temperature
31P NMR spectra were recorded at temperatures ranging
from –30 to +40 °C. At higher temperatures, the minor sig-
nal at 41.1 ppm was observed to increase in intensity, while
at lower temperatures this resonance became less intense and
was not observed below –15 °C. This suggests that an equi-
librium exists between the dimer 10 and the corresponding
12
The reaction of 3 with ZnMe2 in a 2:1 molar ratio pro-
duces a 1:1 mixture of 12 and unreacted 3, indicating that
dimethylzinc in only sufficiently basic to effect monode-
protonation of 3. This result was somewhat surprising, given
that 3 can be triply deprotonated by reactions with n-BuLi at
room temperature; conversely, the trisamidophosphate 1a
can only be dilithiated regardless of reaction conditions,
whereas reactions with dimethylzinc lead to the formation of
triply deprotonated species such as 6 and 7.
1
monomer. The H and 13C NMR spectra of 10 at –30 °C
showed the expected resonances for two inequivalent tert-
butyl environments in a 2:1 ratio, as well as a singlet as-
signed to the two equivalent MeZn+ cations. Thus the low-
temperature NMR spectra are consistent with the presence
of a single species consistent with the solid-state structure of
10.
Conclusions
When the reaction of SP(NH-t-Bu)3 with dimethylzinc
was carried out in a 2:1 molar ratio, a white powder was re-
covered and characterized by multinuclear NMR spectros-
copy and CHN analysis. The 31P NMR spectrum of this
The reactivity of the triamidophosphates EP(NHR)3 (E =
O, S, NSiMe3; R = alkyl) toward dimethylzinc markedly de-
creases on moving from oxygen to the heavier chalcogen
sulfur. The higher basicity of the oxo ligand results in a ten-
dency for coordination to numerous metal centres. Both the
oxygen and sulfur systems display temperature-dependent
solution dynamics. A further decrease in reactivity is ob-
served when the chalcogen atom is replaced by an NSiMe3
group; the only product observed is the monomer {[MeZn]-
[(µ-N-t-Bu)(µ-NSiMe3)P(NH-t-Bu)2]}, presumably because
the steric bulk of the alkylimido groups impedes aggrega-
tion. Curiously, the reactivities of these triamidophosphates
towards n-butyllithium decrease in the reverse order; three-
fold deprotonation of OP(NHR)3 occurs only in reactions
with dimethylzinc. The reactions of other organometallic re-
agents such as MgBu2 with these triamidophosphates is wor-
thy of investigation for comparison with the results observed
for n-BuLi and ZnMe2.
1
product contained a singlet at 42.0 ppm, while the H and
13C NMR spectra revealed two tert-butyl resonances with
relative intensities of 1:2. No resonance for a MeZn+ cation
was observed. These NMR data are consistent with the for-
mation of {Zn[(µ-S)(µ-N-t-Bu)P(NH-t-Bu)2]2} (11) in which
a Zn2+ cation is N,S chelated by two monoanions. A peak at
m/z 607 (M – Me+) is observed in the ESI mass spectrum of
11.
In contrast to the diverse reaction pathways and complex
product mixtures in the reactions of OP(NHR)3 with ZnMe2,
only monodeprotonation is observed in the corresponding re-
action of SP(NH-t-Bu)3. The lower reactivity of 2a toward
ZnMe2 is unexpected, as previous studies have shown this
thiophosphate to be much more reactive toward alkyllithium
reagents than is the oxo analogue 1a (3–5).
© 2005 NRC Canada

1778
Can. J. Chem. Vol. 83, 2005
9. J. Fan, C. Slebodnick, R. Angel, and B.E. Hanson. Inorg.
Chem. 44, 552 (2005).
Acknowledgments
10. Z.-E. Lin, J. Zhang, S.-T. Zheng, and G.-Y. Yang. Z. Anorg.
We thank the University of Calgary and the Natural Sci-
ences and Engineering Research Council of Canada (NSERC)
for funding. The advice of Dr. Dana J. Eisler in the structure
solutions of 5 and 6 is gratefully acknowledged.
Allg. Chem. 631, 148 (2005).
11. A. Kirkpatrick and W.T.A. Harrison. Solid State Sci. 6, 593
(2004).
12. See, for example: S. Oliver, A. Kuperman, and G.A. Ozin.
Angew. Chem. Int. Ed. 37, 47 (1998).
13. A. Altomare, M. Cascarano, C. Giacovazzo, and A. Guagliardi.
J. Appl. Crystallogr. 26, 343 (1993).
14. G.M. Sheldrick. SHELXL-97 [computer program]. University
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© 2005 NRC Canada