Metal selection of ligand functionality in [(mes)2P(- ..O)2Li·2thf]2 and [{(Me3Si)2N}Cd{(mes)2P-..O} 2Li·2thf] (mes = C6H2Me3</su

Article abstract of DOI:10.1039/a608202e

The reaction of LiBuⁿ with [(mes)₂P(H)=O] affords the diorganophosphinate complex [(mes)₂P(^-..O)₂Li·2thf] 1 and [(mes)₂PLi], however, addition of [Cd{N(SiMe₃)₂}_2<

Full text of DOI:10.1039/a608202e

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Metal selection of ligand functionality in [(mes)2P(ÌO)2Li·2thf]2 and
[{(Me3Si)2N}Cd{(mes)2PÌO}2Li·2thf] (mes = C6H2Me3-2,4,6)
Michael A. Beswick, Natalie L. Cromhout, Christopher N. Harmer, Julie S. Palmer, Paul R. Raithby,
Alexander Steiner, Kerry L. Verhorevoort and Dominic S. Wright*
Chemistry Department, University of Cambridge, Lensfield Road, Cambridge, UK CB2 1EW
The reaction of LiBun with [(mes)2P(H)NO] affords the
diorganophosphinate complex [(mes)2P(ÌO)2Li·2thf] 1 and
[(mes)2PLi], however, addition of [Cd{N(SiMe3)2}2] to the
mixture gives the diorganophosphinite complex [{Me3-
of puckered heterocyclic [Cd(PO)2Li] rings, resulting from the
bridging of the Cd and Li centres by the two [(mes)2P(ÌO)]2
ligands. The trigonal-planar Cd centre is attached slightly
unsymmetrically to the P atoms of these bridging ligands [Cd–
P(1) 2.579(5), Cd(1)–P(2) 2.609(3) Å] and to a terminal
(Me3Si)2N group [Cd–N(1) 2.136(7) Å]. Presumably, the
distortion of the [Cd(PO)2Li]2 ring occurs principally in order to
facilitate complexation of the pseudo-tetrahedral Li+ cation by
the O atoms of the [(mes)2PO]2 ligands [1.90(2) Å] (while at
the same time minimising the steric confrontation between the
mesityl groups and the Li-attached thf ligands). Although a
number of transition-metal complexes containing [R2PÌO]2
ligands have been structurally characterised,2,3 2 is the first non-
transition-metal example and, to our knowledge, the first
containing a PV–Cd bond.6
Si)2N}Cd{(mes)2PÌO} Li·2thf] 2; the formation of these
2
complexes illustrates that the ligand functionality of 1 can be
controlled by the character of the coordinated metal ion.
Although a large number of transition- and main-group metal
complexes
containing
diorganophosphinate
ligands,
[R2P(ÌO)2]2, have been structurally characterised,1 only
transition-metal complexes of the diorganophosphinites,
[R2PÌO]2, have so far been investigated.2,3 In comparison to
the variety of metal coordination modes observed for
[R2P(ÌO)2]2 [terminal metal–O, bridging (m-O, m-O), and
bidentate], almost all of the structurally characterised
[R2PÌO]2 complexes contain a (m-O, m-P) metal bridging
mode. Our current interest in this ligand set is in its potential for
forming stabilised main-group metal–P bonded complexes and
heterobimetallic systems. As a prelude to more extensive
studies, we embarked on an investigation of the influence of the
character of main-group metal ions on the coordination mode of
the [R2PÌO]2 ligand.
The occurrence of the [(mes)2P(ÌO)2]2 anion in 1 and the
[(mes)2PÌO]2 anion in 2 can be interpreted in terms of the way
in which the underlying thermodynamics of metal–ligand bond
formation affects the equilibrium between these anions. The
presence of the small, highly charged Li+ cation will tend to
shift this reaction towards the diorganophosphinate, with strong
Li–O bonding being maximised in 1. In 2, the scales are tipped
towards the diorganophosphinite anion since the P/O donor set
offered will provide optimum bonding with the soft Cd and hard
Li metal cations. It is interesting, in the light of this current
work, that the few synthetic studies of the oxidation of metal
diorganophosphides indicate that the hardness or softness of the
metal present has some bearing on the phosphorus oxyanions
produced. Thus, oxidation of [Me2In(PPh2)]2 with pyridine-
We report here the surprising finding that lithiation of
[(mes)2P(H)NO] with LiBun (1:1 equiv.) in thf affords the
diorganophosphinate complex [(mes)2P(ÌO)2Li·thf]2 1. How-
ever, addition of [Cd{N(SiMe3)2}2] to the [(mes)2P(H)NO]–
LiBun mixture gives the heterobimetallic diorganophosphinite
complex [{(Me3Si)2N}Cd{(mes)2PÌO}2Li·2thf] 2.† The very
different ligand functionalities exhibited appear to stem from
the disproportionation reaction of the diorganophosphinite
anion to the diorganophosphinate anion in solution (Scheme
1).‡ Although this disproportionation may be implicated in the
formation of [R2PH] and [R2P(OH)NO] during base hydrolysis
of [R2PCl],4 the metal-dependent selection of these ligands
(observed in 1 and 2) has not previously been reported.
A low-temperature X-ray crystallographic study of 1§ (Fig.
1) shows that the complex has the dimeric structure [(mes)2-
P(ÌO)2Li·2thf]2, composed of planar eight-membered
[LiO2P]2 rings. The Li–O bond lengths in 1 are similar to those
occurring in lithium alkoxides and related compounds (Li–O av.
1.881 Å; cf. range 1.80–2.10 Å for other Li–O bonds).5 The
bridging mode of the [(mes)2P(ÌO)2]2 anion and the dimeric
structure of 1 are typical of a variety of diorganophosphinate
complexes containing a range of main-group and transition
metals.1
N-oxide
gives
the
diorganophosphinate
[Me2In-
{(O)2PPh2}]2,1l whereas the O2 oxidation of [Pd(m-PBut2)(P-
But2H)2] gives the mixed-ligand complex [Pd(But2PO2)(But2-
PO)2H].1o
O(4)
O(3)
Li(1)
O(1)
P(1)
O(2a)
O(1a)
P(1a)
O(2)
Li(1a)
A low-temperature X-ray crystallographic study of 2§ shows
it to have the heterobimetallic structure [{(Me3Si)2N}Cd-
{(mes)2PÌO}2Li·2thf] (Fig. 2). Molecules of 2 are composed
O(4a)
O(3a)
2[(mes)2P–O] –
¨
[(mes)2P] –
[(mes)2P(–O)2] –
¨
+
Fig. 1 Molecular structure of 1. Hydrogen atoms have been omitted for
clarity. Selected bond lengths (Å) and angles (°): P(1)–O(1) 1.501(2),
P(1)–O(2) 1.496(2), Li(1)–O(1) 1.878(4), Li(1)–O(2a) 1.884(4), Li(1)–
O(3,4) 2.05; O(1)–P(1)–O(2) 117.39(9), av. angles about
P(1)–O(1)–Li(1) 140.2(1), P(1)–O(2)–Li(1a) 143.4(1), O(1)–Li(1)–O(2a)
124.4(2), av. angles about Li 107.9.
P 109.4,
SOFT METALS
HARD METALS
Scheme 1
Chem. Commun., 1997
583

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4426 collected reflections, 3518 were independent. The structure was
solved by direct methods and refined by full-matrix least-squares on F2 to
final values of R1 [F > 4s(F)] = 0.064 and wR2 = 0.179 (all data). Largest
peak, hole in the final difference map = 0.805, 21.788 e Å23. Atomic
coordinates, bond lengths and angles, and thermal parameters have been
deposited at the Cambridge Crystallographic Data Centre (CCDC). See
Information for Authors, Issue No. 1. Any request to the CCDC for this
material should quote the full literature citation and the reference number
182/377.
O(2b)
Si(1)
O(1a)
P(2)
Cd
Li(1)
References
N(1)
P(1) O(2a)
1 For examples, see: (a) P. Colamarino, P. L. Orioli, W. D. Benzinger and
H. D. Gillman, Inorg. Chem., 1976, 15, 800; (b) H.-H. Detjen, E. Lindner
and J. Strahle, Chem. Ber., 1978, 111, 2067; (c) A.-F. Shihada and
F. Weller, Z. Anorg. Allg. Chem., 1981, 472, 102; (d) K. W. Oliver,
S. J. Rettig, R. C. Thomas and J. Trotter, Can. J. Chem., 1982, 60, 2017;
(e) R. Cini, P. Orioli, M. Sabat and H. D. Gillman, Inorg. Chim. Acta,
1982, 59, 225; (f) S. Blosl, W. Schwarz and A. Schmidt, Z. Naturforsch.,
Teil B, 1983, 38, 143; (g) J. Haynes, K. W. Oliver, S. J. Rettig,
R. C. Thomson and J. Trotter, Can. J. Chem., 1984, 62, 891; (h)
R. O. Day, J. M. Holmes, V. Chaudrasekhar and R. R. Holmes, J. Am.
Chem. Soc., 1987, 109, 940; (i) R. R. Holmes, K. C. K. Swamy,
C. G. Schmid and R. O. Day, J. Am. Chem. Soc., 1988, 110, 7060; (j)
P. Betz and A. Bino, Inorg. Chim. Acta, 1988, 147, 109; (k) R. O. Day,
V. Chadrasekhar, K. C. K. Swamy, J. M. Holmes, S. D. Burton and
R. R. Holmes, Inorg. Chem., 1988, 27, 2887; (l) A. M. Arif and
A. R. Barron, Polyhedron, 1988, 7, 2091; (m) F. E. Hahn, B. Schneider
and F.-W. Reier, Z. Naturforsch., Teil B, 1990, 45, 134; (n)
K. C. K. Swamy, R. O. Day and R. R. Holmes, Inorg. Chem., 1992, 31,
4184; (o) P. Leoni, F. Marchett and M. Pasquali, J. Organomet. Chem.,
1993, 451, C25.
2 Homonuclear examples, see: G. Munding, B. Schilling, M. Weishaupt,
E. Lindner and J. Strahle, Z. Anorg. Allg. Chem., 1977, 437, 169;
S. Hoehne, E. Lindner and B. Schilling, J. Organomet. Chem., 1977, 139,
315; D. E. Berry, K. A. Beveridge, J. Browning, G. W. Bushnell and
K. K. Dixon, Can. J. Chem., 1986, 64, 1903; D. E. Fogg, N. J. Taylor,
A. Meyer and A. J. Carty, Organometallics, 1987, 6, 2252; N. W. Alcock,
P. Bergamini, T. M. Gomes-Carniero, R. D. Jackson, J. Nicholls,
A. G. Orpen, P. G. Pringle, S. Sostero and O. Traverso, J. Chem. Soc.,
Chem. Commun., 1990, 980; H. Brunner, R. Eder, B. Hammer and
U. Klement, J. Organomet. Chem., 1990, 394, 555; I. J. B. Lin, T. S. Lai,
Ling-Kang Liu and Y. S. Wen, J. Organomet. Chem., 1990, 399, 361;
D. Matt, F. Ingold, F. Balegronne and D. Grandjean, J. Organomet.
Chem., 1990, 339, 349; R. O. Day, P. R. Holmes, A. Schmidpeter,
K. Stoll and L. Howe, Chem. Ber., 1991, 124, 2443; A. Beguin,
H.-C. Bottcher, M. C. Dai, G. Rheingold, H. Stoeckli-Evans, G. Suss-
Fink and B. Watther, Chimia, 1993, 47, 192; U. Florke and H.-J. Haupte,
Z. Kristallogr., 1993, 205, 119; V. Riera, M. A. Ruiz, F. Willafane,
C. Bois and Y. Jeannin, Organometallics, 1993, 12, 124.
Si(2)
O(1b)
Fig. 2 Core structure of 2. Hydrogen atoms have been omitted for clarity.
Selected bond lengths (Å) and angles (°): Cd–N(1) 2.136(7), Cd–P(1)
2.579(3), Cd–P(2) 2.609(3), P(1)–O(1a) 1.512(8), P(1)–O(2a) 1.526(8),
Li(1)–O(1a) 1.90(2), Li(1)–O(2a) 1.90(2), Li(1)–O(1b) 1.95(2), Li(1)–
O(2b) 1.92(2), P(1)–Cd–P(2) 99.9, N(1)–Cd–P(1,2) (av.) 129.9, Cd–
P(1,2)–O(1a,2a) (av.) 106.7, P(1,2)–O(1a,2a)–Li(1) (av.) 122.4, O(1a)–
Li(1)–O(2a) 118(1); av. angles about Li 109.3.
We gratefully acknowledge the EPSRC (M. A. B., C. N. H.,
J. S. P., P. R. R., D. S. W.), the European Union (Fellowship for
A. S.), and The ORS and The Commonwealth Trust (N. L. C.)
for financial support.
Footnotes
† [(mes)2PHNO] was prepared by an alternative method to that reported in
the literature, by the direct hydrolysis of [(mes)2PCl] [generated in situ from
(mes)MgBr and PCl3 (2:1 equiv.) in Et2O] with H2O. The crystalline
phosphinous acid was obtained in 72% yield.
Syntheses: 1: a solution of [(mes)2P(H)NO] (0.57 g, 2.0 mmol) in thf (10
ml) was reacted with LiBun (1.3 ml, 2.0 mmol, 1.6 mol dm23 in hexanes)
under argon. The yellow solution was reduced to dryness under vacuum,
leaving a white solid. The solid was redissolved in hexane (10 ml) and a few
drops of thf (ca. 0.5 ml). Storage at 20 °C (72 h) gave (reproducably) large
crystalline blocks of 1 {first batch, 0.14 g, 16%, based on [(mes)2P(H)NO]
consumed}.
2: a solution of [(mes)2P(H)NO] (1.43 g, 5.0 mmol) in thf (10 ml) was
reacted with LiBun (6.3 ml, 5.0 mmol, 1.6 mol dm23 in hexanes) under
argon. To the yellow solution produced was added neat [Cd{N(SiMe3)2}]
(1.0 ml, 5 mmol). Stirring at room temp. (15 min) gave a colourless solution
which was reduced in vacuo to ca. 10 ml. Storage at 5 °C (24 h), gave air-
sensitive crystalline cuboids of 2 (2.00 g, 80%).
3 Heteronuclear examples, see: J. R. Allen, G. H. W. Milburn, L. Sawyer
and V. K. Shah, Acta Crystallogr., Sect. C, 1985, 41, 58; J. R. Allen,
J. Halfpenny, G. H. W. Milburn and P. M. Veitch, J. Chem. Res., 1986,
279, 2601; P. M.Veitch, J. R. Allen, A. J. Blake and M. Schroder,
J. Chem. Soc., Dalton Trans., 1987, 2853; D. M. Anderson, A. J. Blake,
J. D. Fotheringham, T. A. Stephenson, J. R. Allen and P. M. Veitch, Acta.
Crystallogr., Sect. C, 1988, 44, 1305; U. Kolle, G. Flunkert, R. Gorissen,
M. U. Schmidt and U. Englert, Angew. Chem., Int. Ed. Engl., 1992, 31,
440.
4 (a) Methoden der Organischen Chemie (Houben-Weyl), Phosphor-
Verbindungen I, Georg Theime Verlag, Stuttgart, 1982, vol. E1, p. 242;
H.-J. Kleiner, Liebig Ann. Chem., 1974, 751; Fabw. Hoeschst., Erif:
H.-J. Kleiner and K. Schimmelshmidt, Chem. Abstr., 74 88129K,
1971.
‡ Variable-temperature 31P NMR studies show that the composition of the
LiBun–[(mes)2P(H)NO] reaction mixture is far from simple and that it
changes with ageing. However, the intermediate formation of [(mes)2POLi]
is confirmed by the observation of a weak 1:1:1:1 quartet (d ca. 271.0)
at 280 °C (1J31
ca. 75 Hz). Storage under argon at 20 °C results in
7
P Li
gradual broadening of the resonances originally at d ca. 241 and another
peak at d 2182.4 starts to predominate (after ca. 72 h). This is consistent
with the formation of [(mes)2PLi], produced by the reaction shown in
Scheme 1.
–
§ Crystal data: 1: C52H76Li2O8P2, M = 904.95, triclinic, space group P1,
5 Lithium Chemistry—A Theoretical and Experimental Overview, ed.
A.-M. Sapse and P. von Rague Schleyer, Wiley, New York, 1995, ch. 9
and references therein.
a
= 9.934(3), b = 11.423(4), c = 13.084(5) Å, a = 68.04(4),
b = 68.91(4), g = 71.09(4)°, U = 1233.6(8) Å3, Z = 1, Dc = 1.199 Mg
m23, l = 0.71073 Å, T = 153(2) K, m(Mo-Ka) = 0.138 mm21. Data were
collected on a Siemens-Stoe AED diffractometer using an oil-coated rapidly
cooled crystal8 of dimensions 0.5 3 0.5 3 0.3 mm by the q–w method (3.69
@ q @ 25.02°). Of a total of 5998 collected reflections, 4331 were
independent. The structure was solved by direct methods and refined by
full-matrix least-squares on F2 to final values of R1 [F > 4s(F)] = 0.045
and wR2 = 0.123 (all data);9 largest peak, hole in the final difference
6 There are only a few structurally characterised cadmium diorgano-
phosphide complexes (containing R2P–Cd), see M. A. Matchett,
M. Y. Chiang and W. E. Burho, Inorg. Chem., 1994, 33, 1109; S. C. Goel,
M. Y. Chiang, D. J. Rauscher and W. E. Burho, J. Am. Chem. Soc., 1993,
115, 160; B. L. Benac, A. H. Cowley, R. A. Jones, C. M. Nunn and
T. C. Wright, J. Am. Chem. Soc., 1989, 111, 4986; A. Eicho¨fer,
J. Eisenmann, D. Fenske and F. Simon, Z. Anorg. Allg. Chem., 1993, 691,
1360.
map = 0.285, 20.321 e Å23
.
2: C50H78CdLiNO4P2Si2, M = 994.59, monoclinic, space group C2/c,
a = 14.683(5), b = 22.611(5), c = 17.538(5) Å, b = 114.244(5)°,
U = 5374(3) Å3, Z = 4, Dc = 1.229 Mg m23, l = 0.71073 Å, T = 153(2)
K, m(Mo-Ka) = 0.550 mm21. The procedure was identical to that for 1 with
crystal dimensions 0.3 3 0.2 3 0.2 mm (2.50 @ q @ 22.49°). Of a total of
7 E. Lindner and G. Frey, Chem. Ber., 1980, 113, 2769; 3261.
8 T. Kottke and D. Stalke, J. Appl. Crystallogr., 1993, 26, 615.
9 G. M. Sheldrick, SHELXL-93, Go¨ttingen, 1993.
Received, 4th December 1996; Com. 6/08202E
584
Chem. Commun., 1997