Steric control in the synthesis of phosphinous acid-coordinated mono- and binuclear platinum(II) complexes

3936 Organometallics 2010, 29, 3936–3950

DOI: 10.1021/om100602j

Steric Control in the Synthesis of Phosphinous Acid-Coordinated

Mono- and Binuclear Platinum(II) Complexes

Thierry Achard,^†Laurent Giordano,*^,†Alphonse Tenaglia,^†Yves Gimbert,^‡and

,†

ꢀ

Gerard Buono*

†

ꢀ

ECM, Institut des Sciences Moleculaires de Marseille (ISM2), UMR CNRS 6263,

ꢀ

Universite Aix-Marseille, Avenue Escadrille Normandie Niemen, Case A 62,

F-13397 Marseille Cedex 20, France, and ^‡Deꢀpartement de Chimie Moleꢀculaire,

ꢀ

Universite Joseph Fourier de Grenoble, UMR CNRS5250 ICMG, FR 2607, France

Received June 21, 2010

Several phosphinous acid-coordinated platinum complexes were prepared and characterized. In the

presence of secondary phosphine oxide (2 equiv), PtCl₂(cod) was converted to a series of cis/trans platinum

complexes PtCl₂[R¹R²POH]₂featuring phosphinous acids (PAs) as ligands (20-29). A balance between

the steric and electronic effects of ligands governs their coordination mode. NMR experiments and density

functional theory calculations show that the anti conformer for trans complexes is favored by intramo-

lecular H Cl bonding. PtCl₂[R¹R²POH]₂treated with NEt₃(1 equiv) gave bimetallic platinum

3 3 3

complexes cis-[Pt₂(μ-Cl)₂{(R¹R²PO)₂H}₂] characterized by ³¹P NMR and X-ray diffraction. An unusual

monometallic platinum complex, cis-[PtCl₂{(i-Bu)₂PO}₂H]^-[HNEt₃]^þ(30), was isolated and character-

ized as a possible intermediate in the formation of dinuclear species. Silver acetate and triethylamine both

reacted with PtCl₂[(t-Bu)₂POH]₂to yield new bulky Pt(κ²-acetato){[(t-Bu)₂PO]₂H} platinum complex 31.

The structure of complexes 20d (R¹=Ph, R²=Cy), 21 (R¹=Ph, R²=t-Bu), 21d (R¹=Ph, R²=t-Bu),

24 (R¹=R²=t-Bu), 25 (R¹=R²=Cy),30 (R¹=R²=i-Bu), and 31 (R¹=R²=t-Bu) were determined

by X-ray diffraction.

1. Introduction

phosphinous acids (PAs) R¹R²POH toward transition metal

salts is of interest due to their applications in metal-catalyzed

organic reactions, homogeneous catalysis,^2-12and asym-

metric catalysis using chiral enantiopure secondary phos-

phine oxides (SPOs).³

The coordination chemistry of symmetrically (R¹= R²)

and nonsymmetrically substituted (R¹¼ R²= alkyl, aryl)¹

*To whom correspondence should be addressed. Fax: 33(0)491282742.

E-mail: gerard.buono@univ-cezanne.fr; laurent.giordano@ec-marseille.fr.

(1) For reviews on coordination chemistry of secondary phosphines

see: (a) Roundhill, D. M.; Sperline, R. P.; Beaulieu, W. B. Coord. Chem.

Rev. 1978, 26, 263. (b) Walther, B. Coord. Chem. Rev. 1984, 60, 67.

(c) Appleby, T.; Woollins, J. D. Coord. Chem. Rev. 2002, 235, 121.

(2) (a) van Leeuwen, P. W. N. M.; Roobeek, C. F.; Wife, R. L.;

Frijins, J. H. G. J. Chem. Soc., Chem. Commun. 1986, 1, 31. (b) van

Leeuwen, P. W. N. M.; Roobeek, C. F.; Frjins, J. H. G. Organometallics

1990, 9, 1211. (c) Ghaffar, T.; Parkins, A. W. Tetrahedron Lett. 1995, 36,

8657. (d) Han, L. B.; Tanaka, M. Chem. Commun. 1999, 5, 395. (e) Wicht,

D. K.; Glueck, D. S. In Catalytic Heterofunctionalization; Togni, A.;

Gr€utzmacher, H., Eds.; Wiley-VCH: Weinheim, 2001; Chapter 5. (f) Gobley,

C. J.; van den Heuvel, M.; Abbadi, A.; de Vries, J. G. Tetrahedron Lett.

2000, 41, 2467. (g) Jiang, X. B.; Minaard, A. J.; Hessen, B.; Feringa, B. L.;

Duchateau, A. L. L.; Andrien, J. G. O.; Boogers, J. A. F.; de Vries, J. G. Org.

Lett. 2003, 5, 1503.

(4) (a) Chatt, J.; Heaton, B. T. J. Chem. Soc. (A) 1968, 2745. (b) For a

recent investigation on the tautomerism of secondary phosphane oxides see:

Christiansen, A.; Li, C.; Garland, M.; Selent, D.; Ludwig, R.; Spannenberg,

€

A.; Baumann, W.; Franke, R.; Borner, A. Eur. J. Org. Chem. 2010, 2733.

(5) Gould, R. O.; Jones, C. L.; Sime, W. J.; Stephenson, T. A.

J. Chem. Soc., Dalton Trans. 1977, 669.

(6) (a) Kong, P. C.; Roundhill, D. M. Inorg. Chem. 1972, 11, 749.

(b) Kong, P. C.; Roundhill, D. M. J. Chem. Soc., Dalton Trans. 1974, 187.

(7) Naik, D. V.; Palenki, G. J.; Jacobson, S. E.; Carty, A. J. J. Am.

Chem. Soc. 1974, 96, 2286.

(8) (a) Li, G. Y.; Zheng, G.; Noonan, A. F. J. Org. Chem. 2001, 66,

8677. (b) Li, G. Y.; Marshall, W. J. Organometalics 2002, 21, 590. (c) Li,

G. Y. J. Organomet. Chem. 2002, 653, 63. (d) Li, G. Y. J. Org. Chem. 2002,

67, 3643. (e) Wolf, C.; Lerebours, R. J. Org. Chem. 2003, 68, 7077. (f) Li,

G. Y. US Patent 6124462, 2000; WO01040147, 2001; WO01079213, 2001;

WO02000574, 2002. (g) Li, G. Y. Angew. Chem., Int. Ed. 2001, 40, 1513.

(h) Ackermann, L.; Vicente, R.; Hofmann, N. Org. Lett. 2009, 11, 4274.

(9) Dai, W. M.; Yeung, K. K. Y.; Leung, W. H.; Haynes, R. K.

Tetrahedron: Asymmetry 2003, 14, 2821.

€

(3) For a review see: (a) Dubrovina, N. V.; Borner, A. Angew. Chem.,

Int. Ed. 2004, 43, 5883. (b) Ackermann, L. Synthesis 2006, 1577. (c)

Ackermann, L Synlett 2007, 4, 507. (d) Ackermann, L.; Born, R.; Spatz,

J. H.; Althammer, A.; Gschrei, C. J. Pure Appl. Chem. 2006, 78, 209. (e)

(10) Web page of CombiPhos Catalysts, Inc.: http://www.combi-

€

Ackermann, L. In Phosphorus Ligands in Asymmetric Catalysis; Borner,

phos.com/.

A., Ed.; Wiley-VCH: Weinheim, 2008; Vol. 2, pp 831-847. (f) Gatineau,

(11) (a) The first Pt complex was reported by: Grinberg, A. A.;

Troiskaya, A. D. Bull. Acad. Sci. USSR 1944, 178. (b) Bergamini, P.;

Bertolasi, V.; Cattabriga, M.; Ferretti, V.; Loprieno, U.; Mantovani, N.;

Marvelli, L. Eur. J. Inorg. Chem. 2003, 918. (c) For the recent reaction of

SPO with rhodium(I) see: Christiansen, A.; Selent, D.; Spannenberg, A.;

€

D.; Moraleda, D.; Naubron, J.-V.; Burgi, T.; Giordano, L.; Buono, G.

Tetrahedron: Asymmetry 2009, 20, 1912. (g) Chan, E. Y. Y.; Zhang, Q.-F.;

Sau, Y.-K.; Lo, S. M. F.; Sung, H. H. Y.; Williams, I. D.; Haynes, R. K.;

Leung, W. H. Inorg. Chem. 2004, 43, 4921. (h) Nemoto, T.; Jin, L.;

Nakamura, H. Tetrahedron Lett. 2006, 47, 6577. (i) Jiang, X.; van den

Berg, M.; Minnaard, A. J.; Feringa, B. L.; de Vries, J. G. Tetrahedron:

Asymmetry 2004, 15, 2223.

€

Baumann, W.; Franke, R.; Borner, A. Organometallics 2010, 29, 3139.

(12) Jiang, X.; Minnaard, A. J.; Feringa, B. L.; de Vries, J. G. J. Org.

Chem. 2004, 69, 2327.

r

pubs.acs.org/Organometallics

Published on Web 08/11/2010

2010 American Chemical Society

Article

Organometallics, Vol. 29, No. 17, 2010 3937

Scheme 1. SPOs as L-Type Preligands, L = PA

Figure 1. Li’s Combiphos catalysts.

The structures of several platinum complexes have been

characterized by X-ray analysis.

2. Results and Discussion

2.1. Synthesis of Secondary Phosphine Oxides. Secondary

phosphine oxides are valuable intermediates in phosphorus

chemistry, especially used as precursors of tertiary phosphine

oxides.¹⁷Several preparative methods of symmetrically sub-

stituted SPOs have been developed; for instance, hydrolysis of

R₂PY (Y = Cl¹⁸or NR⁰₂¹⁹), addition of Grignard reagents to

dialkylphosphites,²⁰reduction of phosphoryl chlorides,^18a,20a,21

oxidation of secondary phosphines,²²or reductive cleavage

of tertiary phosphine oxides²³are among the most relevant

methods. Most of the syntheses have been described in

homogeneous media^24,25and involved multistep routes. In

contrast with these procedures, Li’s group reported an inter-

esting synthesis of SPOs based on the cleavage of the P-N

bond of polymer-supported aminophosphines.^8fFor our pur-

pose, the following set of SPOs was selected (Figure 3) to

prepare several platinum complexes and study their coordina-

tion chemistry.

In 1968, Chatt and Heaton reported that in solution

secondary phosphine oxide 1 is in equilibrium with phosphi-

nous acid 2. PAs are appropriate to coordinate transition

metal complexes through phosphorus P(III) form (Scheme 1);⁴

therefore SPOs may be considered as L-type preligands

(Scheme 1).^3a,iIn the presence of base, type I complexes

3

containing two PA ligands can be converted into type II

complexes in which the PA and R¹R²PO^-are in a cis relation-

ship and strongly linked through a hydrogen bond.^1,5In such

events, the PAs act similarly to bidentate ligands. Alterna-

tively, type II complexes have also been prepared by treatment

7

of R₂P-X (X = Cl,⁴R⁰O,^5,6or CtCCF₃) with a metal salt in

the presence of water.

Palladium complexes containing PA ligands have been

widely studied in the past decade. These complexes, now

commercially available, are highly efficient catalysts⁸in various

cross-coupling reactions (Suzuki,^8d,eHeck,^8a,fKumada,^8b,c

Negishi,^8dand Stille^8e), hydroformylation reactions,²and

asymmetric allylic substitution.⁹Recently, Li reported that

POPd complexes¹⁰(Figure 1) are particularly efficient catalysts

in C-C, C-N,^8a,e,fand C-S^8a,d,ebond-forming reactions.

In contrast, very little was reported for the synthesis of

similar platinum PA complexes.¹¹Mononuclear complexes 3

and 4 (Figure 2) are known to catalyze hydrolysis of nitriles

to amide compounds^2a,c,12,13and hydroformylation.^2a,b,14

Recently our group reported the synthesis of dinuclear

palladium complexes (PAPd) derived from SPOs and their

applications as catalysts in a formal [2þ1] cycloaddition

between bicyclic alkenes and alkynes.¹⁵A similar reaction

was observed with the mononuclear Pt complex 5.¹⁶

(17) (a) Methods of Preparation of Phosphine Chalcogenides: Bhat-

tacharya, A. K.; Roy, N. K. In The Chemistry of Organophosphorous

Compounds, Vol. 2; Hartley, F. R, Ed.; Wiley: Chichester, 1992; pp

195-285. (b) Edmundson, R. S. Chemical Properties and Reactions of

Phosphine Chalcogenides. In The Chemistry of Organophosphorous

Compounds, Vol. 2; Hartley, F. R., Ed.; Wiley: Chichester, 1992; pp

287-407.

(18) (a) Miller, R. C. J. Org. Chem. 1959, 24, 2013. (b) Derkach, G. I.;

Kirsanov, A. V. Chem. Abstr. 1960, 54, 8682. (c) Walling, C. Chem. Abstr.

1948, 42, 4199; DuPont, Patent AP2437798, 1944. (d) Rabinowitz, R.;

Pellon, J. J. Org. Chem. 1961, 26, 4623. (e) Henderson, W. A.; Mitarbb, H.

J. Org. Chem. 1961, 26, 4770. (f) ICI, Patents FP1252545, 1266196, 1960.

(19) From phosphorus ester: (a) Sander, M. Chem. Ber. 1960, 93,

1220. (b) Kabachnik, M. I.; Cvetkov, E. N. Chem. Abstr. 1961, 55, 14288.

From phosphorus amides: (c) Burg, A. B.; Slota, P. J., Jr. J. Am. Chem. Soc.

1958, 80, 1107. Burg, A. B.; Slota, P. J., Jr. J. Am. Chem. Soc. 1960, 82,

2148. (d) Burg, A. B.; Wagner, R. I. Chem. Abstr. 1960, 54, 18437; AP,

Patent 2934564, 1957. (e) Seidel, W.; Issleib, K. Chem. Ber. 1959, 92,

2681.

(20) (a) Williams, R. H.; Hamilton, L. A. J. Am. Chem. Soc. 1952, 74,

5418. Williams, R. H.; Hamilton, L. A. J. Am. Chem. Soc. 1955, 77, 3411.

(b) Miller, R. C.; Bradley, J. S.; Hamilton, L. A. J. Am. Chem. Soc. 1956,

78, 5299. (c) Hunt, B. B.; Saunders, B. C. J. Chem. Soc. 1957, 2413. (d)

Williams, J. L. Chem. Ind. 1957, 235. (e) For a general method see: Busacca,

C. A.; Lorenz, J. C.; Grinberg, N.; Haddad, N.; Hrapchak, M.; Latli, B.; Lee,

H.; Sabila, P.; Saha, A.; Sarvestani, M.; Shen, S.; Varsolona, R.; Wei, X.;

Senanayake, C. H. Org. Lett. 2005, 7, 4277.

(21) Horner, L.; Beck, P.; Toscano, V. G. Chem. Ber. 1961, 94, 1317.

(22) (a) Rauhut, M. M.; Mitarbb, H. J. Am. Chem. Soc. 1958, 80,

6690. (b) Rauhut, M. M.; Currier, H. A. J. Org. Chem. 1961, 26, 4626. (c)

Patent, AP2953596, 1958. (d) Patent, GE1104957, 1959. (e) Hechenbleikner,

I.; Currier, H. A. Chem. Abstr. 1961, 55, 4363.

Herein, we report a general study on the coordination

behavior of PAs to platinum complexes and the synthesis of

PA mononuclear (type I, n = 2), PA binuclear (type II), and

κ²-acetato PA mononuclear platinum (type II) complexes

(see Scheme 1). We show that the formation of these com-

plexes is highly dependent on the steric properties of the PAs.

(13) (a) Jensen, C. M.; Trogler, W. C. J. Am. Chem. Soc. 1986, 108,

723. (b) Ghaffar, T.; Parkins, A. W. J. Mol. Catal. A 2000, 160, 249.

(14) (a) Van Leeuwen, P. W. N. M.; Roobeek, C. “Process for the

hydroformylation of olefins. US Patent 4408078, 1983. (b) Van Leeuwen,

P. W. N. M.; Roobeek, C. F. In Homogeneous Transition Metal Catalysis

Reactions; Advances in Chemistry Series 230; 1992; p 367.

(15) (a) Bigeault, J.; Giordano, L.; Buono, G. Angew. Chem., Int. Ed.

2005, 44, 4753. (b) Bigeault, J.; de Riggi, I.; Gimbert, Y.; Giordano, L.;

Buono, G. Synlett 2008, 1071.

(16) (a) Bigeault, J.; Giordano, L.; De Riggi, I.; Gimbert, Y.; Buono,

G. Org. Lett. 2007, 9, 3567–3570. (b) Analogous Pd acetato complexes have

been used with success in catalysis (see refs ^3f, 15a, 15b). (c) Recently, the

monomeric palladium(κ²-acetato){[R₂PO]₂H} complex in which R is an

adamantyl substituent was isolated and structurally characterized by X-ray

diffraction. Ackermann, L.; Potukuchi, H. K.; Kapdi, A. R.; Schulzke, C.

Chem.;Eur. J. 2010, 16, 3300.

(23) Hoffmann, A. K.; Tesch, A. G. J. Am. Chem. Soc. 1959, 81, 5519.

(24) (a) Angstadt, H. P. J. Am. Chem. Soc. 1964, 86, 5040. (b) Crofts,

P. C.; Parker, D. M. J. Chem. Soc. C 1970, 332. (c) Dahl, O. J. Chem. Soc.,

Perkin Trans. 1 1978, 9, 947. (d) Gomelya, N. D.; Feshchenko, N. G. Zh.

Obshch. Khim. 1987, 57, 1702. (e) Goerlich, J. R.; Fischer, A.; Jones, P. G.;

Schmutzler, R. Z. Naturforsch. B 1994, 49, 801. (f) Dmitriev, T. J. Gen.

Chem. USSR (Engl. Transl.) 1978, 48, 1405. (g) Dmitriev, T. Zh. Obshch.

Khim. 1978, 48, 1533.

(25) (a) Hays, H. R. J. Org. Chem. 1968, 33, 3690. (b) Harger, M. J. P.;

Westlake, S. Tetrahedron 1982, 38, 1511.

3938 Organometallics, Vol. 29, No. 17, 2010

Achard et al.

Figure 2. Phosphinous acid platinum and palladium complexes.

Furthermore enantiopure diastereomers 19 have been success-

fully used for the synthesis of enantioenriched SPO.²⁹

2.2. Synthesis of Platinum Complexes. Recently, our

group reported the synthesis of new monuclear platinum(II)

complexes featuring κ²carboxylate ligands such as Pt(κ²-

acetato){[RPhPO]₂H} and their use as catalysts in the ben-

zylidenecyclopropanation of norbornene derivatives.¹⁶

These platinum complexes were easily obtained in two steps.

First, PtCl₂(cod) was treated with 2 equiv of RPhP(O)H in

refluxing THF. The ³¹P NMR spectrum of the crude reac-

tion mixture revealed two sets of signals indicative of cis and

trans complexes PtCl₂[RPhPOH]₂as a mixture of meso and dl

stereoisomers. A cis/trans mixture of PtCl₂[RPhPOH]₂inter-

mediates (20-23) obtained after evaporation of the solvent

was used in the next step without further purification. Addition

of AgOAc (2 equiv) at room temperature to the mixture

afforded after purification by chromatography Pt(κ²-acetato)-

{[RPhPO]₂H} complexes (Scheme 4).

Figure 3. Selected secondary phosphine oxides.

Scheme 2. Synthesis of SPOs 6 and 7

Scheme 3. Synthesis of SPOs 11-14

When PtCl₂(CH₃CN)₂was used as the platinum source

with 2 equiv of enantiopure (R)-(þ)-tert-butylphenylpho-

sphine oxide 11, a single trans complex, (þ)-21, was obtained

with partial racemization.¹⁶Interestingly, when the reaction

was carried out with PtCl₂(cod) at room temperature for 12 h

in CH₂Cl₂, a 1:1 mixture of cis- and trans-21 was obtained

with almost no racemization.

Following these preliminary results, we have retained

PtCl₂(cod) for the synthesis of PtCl₂complexes 20 to 28.

These platinum complexes were investigated in order to

establish the coordination mode of PA ligands.

Di-tert-butylphosphine oxide 6, which is known to be

among the best SPO preligands in metal-catalyzed cross-

coupling reactions, was readily prepared by addition of tert-

butyllithium on commercially available diphenylphosphite

(Scheme 2).

Dicyclohexylphosphine oxide 7 was prepared similarly

from cyclohexylmagnesium chloride. Both 6 and 7 were

conveniently purified on deactivated silica (20% H₂O, 80/

20 petroleum ether (PE/Et₂O) in 72% and 60% yields,

respectively.

2.3. PA Coordination Behavior toward Platinum Salts (³¹P

NMR Study). At the outset, we studied the coordination

mode of the PA from racemic preligand 12 on the platinum

center. The NMR studies of platinum complexes were

performed with PtCl₂(cod) because of its higher solubility

in most of the solvents in regard to PtCl₂(CH₃CN)₂and

PtCl₂.

A solution of racemic SPO 12 in dry DCM was added to a

solution of PtCl₂(cod) in DCM at room temperature, and the

solution mixture was warmed to 40 °C. The reaction was

Phosphine oxides 8, 9, and 10 were obtained by reaction of di-

ethylphosphite with the corresponding Grignard reagent or orga-

nolithium compounds according to established procedures.^25a

Various methodologies are available for the synthesis of

racemic SPOs.²⁶Nonsymmetrically substituted SPOs R¹R²-

P(O)H 11-13 were prepared according to the Emmick²⁷

procedure from ethylphenylphosphinate 17 (Scheme 3). SPO

14 was obtained by a slight modification procedure from a

mixture of (L)-menthylphenylphosphinate 19 diastereomers.²⁸

(29) Recent preparation of optically active SPOs from (L)-menthol:

(a) Leyris, A.; Bigeault, J.; Nuel, D.; Giordano, L.; Buono, G. Tetra-

hedron Lett. 2007, 48, 5247. (b) Xu, Q.; Zhao, C. Q.; Han, L. B. J. Am.

Chem. Soc. 2008, 130, 12648. Other preparations of optically active SPOs:

(c) Pietrusiewicz, K. M.; Zablocka, M. Chem. Rev. 1994, 94, 1375. (d) Holt,

J.; Maj, A. M.; Schudde, E. P.; Pietrusiewicz, K. M.; Sieron, L.; Wieczorek,

W.; Jerphagnon, T.; Arends, I.; Hanefeld, U.; Minnaard, A. J. Synthesis 2009,

12, 2061. (e) Haynes, R. K.; Au-Yeung, T. L.; Chan, W. K.; Lam, W. L.; Li,

Z. Y.; Yeung, L. L.; Chan, A. S. C.; Li, P.; Koen, M.; Mitchell, C. R.;

Vonwiller, S. C. Eur. J. Org. Chem. 2000, 3205. (f) Leyris, A.; Nuel, D.;

Giordano, L.; Achard, M.; Buono, G. Tetrahedron Lett. 2005, 46, 8677. (g)

Michalski, J.; Skrzypzynski, Z. J. Organomet. Chem. 1975, 97, C31–C32.

(h) Dubrovina, N. V.; Jiao, H. J.; Tararov, V. I.; Spannenberg, A.; Kadyrov, R.;

Monsees, A.; Christiansen, A.; Borner, A. Eur. J. Org. Chem. 2006, 15,

3412. (i) Wang, F.; Polavarapu, P. L.; Drabowicz, J.; Mikolajczyk, M. J. Org.

Chem. 2000, 65, 7561. (j) Gallagher, M. J. In The Chemistry of the

Organophosphorus Compounds; Hartley, F. R., Ed.; John Wiley & Sons:

Chichester, 1992; Vol. 2, pp 53-76.

(26) Quin, L. D. A Guide to Organophosphorus Chemistry; Wiley-

Interscience: New York, 2000.

(27) (a) Emmick, T. L.; Letsinger, R. L. J. Am. Chem. Soc. 1968, 90,

3459. (b) Shioji, K.; Tsukimoto, S.; Tanaka, H.; Okuma, K. Chem. Lett.

2003, 32, 604.

(28) (a) Famham, W. B.; Murray, R. K.; Mislow, K. J. Am. Chem.

Soc. 1970, 92, 5809. (b) Reiff, L. P.; Aaron, H. S. J. Am. Chem. Soc. 1970,

92, 5275. (c) Benschop, H. P.; Platenburg, D. H. J. M.; Meppelder, F. H.;

Boter, H. J. Chem. Commun. 1970, 33. (d) Bodalski, R.; Koszuk

Phosphorus, Sulfur, Silicon Relat. Elem. 1989, 44, 99.

Article

Organometallics, Vol. 29, No. 17, 2010 3939

Figure 4. Progress of the reaction between PtCl₂(cod) and SPO 12 monitored by ³¹P{¹H} NMR (CDCl₃).

Scheme 4. Synthesis of (K²-Acetato) Platinum Complexes

monitored by ³¹P NMR using a capillary C₆D₆as the

external lock (Figure 4). All the spectra were obtained at

room temperature and recorded after 128 scans, and the

chemical shifts were not corrected. The expected ³¹P{¹H}

NMR spectrum with ¹⁹⁵Pt satellites for one diastereomer

platinum complex A showed a centered signal and a doublet

due to the J_P-Pt. The direct assignment cis and trans config-

urations is based on the J values between platinum and

phosphorus. The trans complexes reveal typical values

around 2500 Hz for J_Pt-P, whereas cis complexes show J_Pt-P

values around 4000 Hz.³⁰

ppm (J_Pt-P= 4026 Hz) and 80.4 ppm (J_Pt-P= 4024 Hz),

respectively (Figure 4a). Uncoordinated SPO 12 (δ 40 ppm)

and other platinum species (B) were also detected. After

135 min, the spectrum is greatly simplified, and the cis com-

plex A was observed at 79-80 ppm with traces of both free

SPO and complex B at δ 81 ppm (J=3282 Hz) (Figure 4b).

After 280 min, we observed a total consumption of SPO and

disappearance of B to form exclusively the cis platinum com-

plex A as a 1:1 mixture of meso/dl diastereomers (Figure 4c).

After 280 min, addition of NEt₃(1 equiv) as the hydro-

chloride scavenger afforded a new cis-dimeric platinum com-

plex C as a mixture of meso and dl diastereomers located at δ

59.2 and 60.5 with J_Pt-Pvalues of 3965 and 3946 Hz, respec-

tively (Figure 4d).

At 30 min, the formation of cis complex A as the major

species was observed around 79-80 ppm as a mixture of cis-

dl [(R_P*,R_P*)] and cis-meso [(R_P*,S_P*)] complexes at δ 79.6

A mixture of SPO 12 and PtCl₂(cod) refluxed for 16 h in

THF led to the formation of complex cis-20 and dimer cis-

20d in a 1.8:1 ratio. When the same reaction was conducted

for 5 days, the cis dimer 20d was formed exclusively. Similar

results were observed when the reaction was carried out

in DCM or acetonitrile. Consequently the cis dimer 20d

appeared to be the thermodynamic compound. It is worth-

while to note that the formation of 20d occurred even in

the absence of NEt₃, but in this case, release of HCl in the

reaction media occurred with the formation of minor side

phosphorus products.

(30) The structures of complexes were deduced from coupling con-

stants between platinum and phosphorus atoms. For the cis isomer, the

¹J

coupling constant is larger (≈3700 Hz) than that for the trans

¹⁹⁵Pt-P

isomer (≈2500 Hz). For a ³¹P NMR study of tertiary phosphine com-

plexes of platinum(II), see: (a) Grim, S. O.; Keiter, R. L.; McFarlane, W.

Inorg. Chem. 1967, 6, 1133. (b) Cobley, C. J.; Pringle, P. G. Inorg. Chim. Acta

1997, 265, 107. (c) Pregosin, P. S. ; Kunnz, R. W., P.; Fluck, E.; Kosfeld, R.,

Eds. ³¹P and ¹³C of Transition Metal Complexes; Springer: New York, 1979.

(d)Mather, G. G.;Pidcocok, A.;Rapsey, G. J. N. J. Chem. Soc., Dalton Trans.

1973, 2095. (e) Crispini, A.; Harisson, K. N.; Orpen, A. G.; Prongle, P. G.;

Wheatcroft, J. R. J. Chem. Soc., Dalton Trans. 1996, 1069. (f) Payne, N. C.;

Stephan, D. W. J. Organomet. Chem. 1981, 221, 203.

3940 Organometallics, Vol. 29, No. 17, 2010

Achard et al.

Scheme 5. Synthesis of Mononuclear Type I cis, trans Platinum

Complexes

but favored the exclusive formation of trans complex 21.

Indeed in this configuration, nonbonded interactions bet-

ween the two bulky t-Bu groups on the phosphorus atoms

are minimized (Figure 7b). The observed configurations of

these complexes reflect the delicate balance between the

electronic and steric effects. Fornonsymmetricalphosphinous

acid complexes, the stereochemistry of the product depends

on a competition between electronic effects induced by the

phenyl group and steric hindrance of the alkyl group. The

formation of cis complexes is governed by the electronic

effects of the substituents, while the predominance of steric

effects of substituents led to the trans configuration.^31,32

After 12 h of reaction (Table 1, entry 1), the ³¹P NMR

spectrum of 24 showed two signals with satellites at δ 109.4

and 110.3 ppm (7.7:1 ratio) (Figure 5), corresponding to anti

(J_Pt-P2409 Hz) and syn (J_Pt-P2432 Hz) trans complexes,

respectively. This assignment is based on NMR data re-

ported by Mastorilli et al.³³for the platinum complex 29

in equilibrium between syn/anti conformations (anti/syn =

1.2) (Scheme 6). These conformers showed a coupling con-

stant of J_Pt-P= 2429 Hz for syn-29 and J_Pt-P= 2421 Hz for

anti-29.

Table 1. Synthesis of Mononuclear Platinum Complexes

entry

complex

R¹

R²

time

cis/trans

yield

1

2

3

4

5

6

7

8

24

25

26

27

28

20

21

22

23

t-Bu

Cy

t-Bu

Cy

Ph

Me

i-Bu

Cy

t-Bu

Me

12

20

12

24

16

12

24

0:1^a

0:1^b

0:1

1:0

1.6:1

0:1

1:0

>99

Ph

d

Me

i-Bu

Ph

DFT calculations³⁴revealed no significant Gibbs energy

difference between the syn and anti conformers for com-

pound 29, while for compound 24, the calculated energy

d

9

10

11

>99^c

difference of 1.1 kcal mol^-1favors the anti conformer.

d

3

Ph

d

When the reaction of PtCl₂(cod) with t-Bu₂P(O)H 6 was

refluxed for 20 h in THF, stereoisomer anti-trans 24 (Table 1

entry 2) was observed exclusively by ³¹P NMR (Figure 5).

Interestingly, a mixture of syn/anti-24 after reflux led only to

the thermodynamically more stable anti isomer. X-ray dif-

fraction analysis showed unambiguously the anti conformer

platinum complex 24 (Figure 6).

i-Bu

1:0

^asyn/anti: 1:7.7. ^bOnly anti. ^c30% yield of meso-crystal. ^dNot iso-

lated. 100% conversion was observed in all cases.

2.4. Synthesis of Mononuclear Type I Platinum Complexes.

Having identified THF as the optimal solvent, the synthesis of

platinum complexes coordinated to symmetrical and non-

symmetrical racemic PAs was undertaken from PtCl₂(cod)

with SPOs preligands (2 equiv) in refluxing THF for 12-16 h

(Scheme 5). The results are reported in Table 1.

2.4.1. Crystal Structure of Complexes 21, 24, and 25.

Suitable crystals were obtained by slow diffusion (hexane/

CH₂Cl₂solution) for complexes 24, 21, and 25, which were

characterized by X-ray diffraction analysis.³⁵These com-

plexes showed square-planar complexes with a platinum(II)

center coordinated with two PA ligands. Unexpectedly,

partial crystallization of 21 (as a diastereomeric mixture)

allowed isolation of pure crystals for diastereomer (R*,S*)-

21 (Figure 7b).

SPOs 6 and 7, with bulky alkyl groups such as t-Bu and Cy

on the phosphorus atom, allowed the quantitative formation

of mononuclear trans platinum complexes 24 and 25 exclu-

sively (Table 1 entries 1, 2, and 3). The trans configuration for

these complexes was easily deduced with ³¹P NMR spectro-

scopy (J_Pt-P≈ 2500 Hz) (Figure 5) and secured by X-ray

diffraction analyses (Figures 6 and 7a). Complexes 26 and

27, with smaller groups on the phosphorus atom, were

obtained exclusively in a cis configuration according to ³¹P

NMR data (J_Pt-P≈ 4000 Hz) (see Table 1, entries 4 and 5).

These complexes were obtained in high chemical yields but

contaminated with trace amounts of unreacted PtCl₂(cod)

complex. Use of a slight excess of SPO drove the reaction to

the formation of platinum complexes containing two and

three phosphinous acid ligands. The coordination of the

third SPO ligand onto the metal was possible thanks to the

smaller size of the alkyl groups bound to the phosphorus

atom.^12,14A SPO with a medium-sized groups (such as i-Bu)

led exclusively to the formation of cis complex 28.

Structural data of various trans-Pt(II) dichloride com-

plexes with phosphorus ligands, provided by the Cambridge

Structural Database (CSD),³⁶were examined in order to

(32) Crabtree, R. H. The Organometallic Chemistry of The Transition

Metals, 4th ed.; Wiley: New York, 2009.

(33) Giannandrea, R.; Mastrorilli, P.; Palma, M.; Fanizzi, F. P.;

Englert, U.; Nobile, C. F. Eur. J. Inorg. Chem. 2000, 12, 2573.

(34) DFT computations were carried out using the B3LYP functional

as implemented in Gaussian. The platinum atom was described by a

double-ζ basis set (SDD),^34aand the 6-31G(d,p) basis set^34b-fwas used

for the other elements. (a) Kuechle, W.; Dolg, M.; Stoll, H.; Preuss., H.

Mol. Phys. 1991, 74, 1245. (b) Ditchfield, R.; Hehre, W. J.; Pople, J. A. J.

Chem. Phys. 1971, 54, 724. (c) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J.

Chem. Phys. 1972, 56, 2257. (d) Hariharan, P. C.; Pople, J. A. Theor. Chim.

Acta 1973, 28, 213. (e) Hariharan, P. C.; Pople, J. A. Mol. Phys. 1974, 27,

209. (f) Gordon, M. S. Chem. Phys. Lett. 1980, 76, 163.

Phosphines bearing both alkyl and aryl groups at the

phosphorus atom afforded generally cis complexes.³¹

A

similar behavior was observed for nonsymmetrical SPOs 12

(Ph, Cy), 13 (i-Bu, Ph), and 14 (Ph, Me), providing only cis

complexes 20, 23, and 22, respectively. In contrast, pre-

ligand SPO 11 (Ph, t-Bu) did not provide the cis complex

(35) The crystallographic data for complexes 21 (CCDC 771346), 24

(CCDC 771340), and 25 (CCDC 771345) have been deposited with the

Cambridge Crystallographic Data Centre. These data can be obtained

free of charge at www.ccdc.ac.uk/data\request/cif.

(36) Cambridge Structural Database System, Cambridge Crystal-

lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.

Redman, J.; Willett, P.; Allen, F. H.; Taylor, R. A Citation Analysis of

the Cambridge Crystallographic Data Centre. J. Appl. Crystallogr.

2001, 34, 375.

(31) Belluco, U. Organometallic and Coordination Chemistry of Pla-

tinum; Academic Press: London, 1974.

Article

Organometallics, Vol. 29, No. 17, 2010 3941

Figure 5. ³¹P NMR (CDCl₃) spectra of 24. J_Pt-Panti= 2409 and J_Pt-Psyn= 2432 Hz.

Figure 6. PLUTO representation of the X-ray crystal structure of anti-24. Most of the hydrogen atoms are omitted for clarity.

Scheme 6. syn/anti Equilibrium for Complex 29

˚

bond for complexes 21, 24, and 25 (2.308 A) is in agreement

with values for trans PtCl₂L₂(L = phosphorus ligand)

˚

complexes (average ≈ 2.305 A, Figure 8a). Similarly the Pt-P

˚

bond length average (2.324 A) is in agreement with the Pt-P

average value (2.320 A, Figure 8b) for trans PtCl₂L₂. For

˚

Figure 7. PLUTO representation of the X-ray crystal structure of

25 and (R*_P,S*_P)-21. Most hydrogen atoms are omitted for clarity.

example, the corresponding values in several complexes con-

˚

taining a trans Cl-Pt-Cl are in the range 2.266 to 2.379 A

evaluate and compare standard Pt-P and Pt-Cl bond

lengths (Figure 8a and b). The average length of the Pt-Cl

and 2.25 to 2.42 A for trans P-Pt-P.^33,37In platinum square-

˚

planar complexes Pt-Cl bond lengths are between 2.276(3) and

2.313(2) A (Table 2).³⁸The slightly larger P(1)-Pt-Cl(2) angles

˚

(37) (a) Croxtall, B.; Fawcett, J.; Hope, E. G.; Stuart, A. M. J. Chem.

Soc., Dalton Trans. 2002, 4, 491. (b) Giannandrea, R.; Mastrorilli, P.;

Nobile, C. F. Inorg. Chim. Acta 1999, 284, 116. (c) Colbran, S. B.; Craig,

D. C.; Sembiring, S. B. Inorg. Chim. Acta 1990, 176, 225. (d) Sembiring,

S. B.; Colbran, S. B.; Bishop, R.; Craig, D. C.; Rae, A. D. Inorg. Chim. Acta

1995, 228, 109. (e) Aljibori, S.; Crocker, C.; McDonald, W. S.; Shaw, B. L. J.

Chem. Soc., Dalton Trans. 1981, 12, 2589. (f) Hursthouse, M. B. X-ray CSD

IPOPEI from Cambridge database ; Department of Chemistry, University of

Cardiff. (g) Coleman, K. S.; Holloway, J. H.; Hope, E. G.; Russell, D. R.;

Saunders, G. C. Polyhedron 1995, 14, 2107. (h) Gallo, V.; Latronico, M.;

Mastrorilli, P.; Nobile, C. F.; Suranna, G. P.; Ciccarella, G.; Englert, U. Eur. J.

Inorg. Chem. 2005, 22, 4607.

in comparison with P(1)-Pt-Cl(1) angles accommodate an

intramolecular hydrogen bonding (O-H Cl) (Table 3).

3 3 3

These two hydrogen bonds stabilize the “spiro” structure with

two five-membered rings centered on the platinum atom.

˚

The average P-O bond lengths of 1.609 A for these

three complexes are slightly longer in comparison with

(38) Allen, F. H. Acta Crystallogr., Sect. B: Struct. Sci. 2002, B58,

380.

3942 Organometallics, Vol. 29, No. 17, 2010

Achard et al.

Figure 8. Histograms of Pt-Cl (a) and Pt-P (b) bond length distribution in trans PtCl₂L₂complexes (L = phosphorus ligand)

provided by CSD.

˚

Table 2. Selected Bond Lengths [A] and Angles [deg] for Com-

pounds trans-21, 24, and 25 with Estimated Standard Deviations

in Parentheses

Scheme 7. Synthesis of Dinuclear Platinum Complexes

bond

trans-21

trans-24

trans-25

Pt1-Cl1

Pt-P1

2.3112 (14)

2.3276 (12)

1.607(4)

88.23(5)

91.77(5)

2.3096 (18)

2.3379 (16)

1.613(5)

88.77(6)

91.22(6)

2.3054 (11)

2.3065 (10)

1.608(3)

89.28(4)

90.72(4)

P1-O1

P1-Pt-Cl1

P1-Pt-Cl2

˚

Table 3. Hydrogen Bond Lengths (A) and Angles (deg) of

21, 24, and 25

complex

D-H

A

D-H

H

A

D

A

D-H

3 3 3

A

3 3 3

21

24

25

O1-H Cl1

0.820

0.821

0.820

2.227

2.309

2.231

2.940

3.008

2.944

145.61

143.41

145.56

H-bond involving the oxygen atom of tetrahydrofuran

˚

(OH---O = 1.902 A). For structures 21, 24, and 25 two

3 3 3

O1-H Cl1

3 3 3

O1-H Cl1

3 3 3

similar intramolecular hydrogen bonds with chlorine

˚

atoms (O-H Cl range 2.94-3.00 A, Table 3) were ob-

corresponding lengths in the cis-[PtCl₂(Ph₂POH)₂] monomer

complex^39aand complexes featuring a P-O---H---O-P in-

teraction such as cis-[Pt₂(μ-Cl)₂{(Ph₂PO)₂H}₂] (1.547 A),

3 3 3

served. These values are in agreement with a wide range of

˚

11b

˚

O-H Cl hydrogen bonds (2.86-3.21 A) reported by

3 3 3

Stout and Jensen.⁴⁵

7

˚

[Pd₂(μ-SCN)₂{(Ph₂PO)₂H}₂] (1.543 A), (Pd(S₂PMe₂){(Ph₂-

PO)₂H)] (1.545 A), [Mo(CO)₄(Ph₂PO)₂H}]^-(1.562 and

40

˚

2.5. Dinuclear Platinum Type II Chloro-Bridged Complexes.

Treatment of a mixture of cis and/or trans (PA)₂PtCl₂with

triethylamine generates cleanly dinuclear complexes 20d-23d

and 26d,27d (Scheme 7). ³¹P NMR of these complexes revealed

signals ranging from 53 to 65 ppm (Table 4) characteristic of cis

dimer platinum structures. Although different diastereomeric

complexes⁴⁶could be formed from racemic SPOs, only meso

and dl complexes are observed.

2.5.1. X-ray Crystal Structure of meso-[(R*_P,S*_P),(R*_P,

S*_P)]-20d. Complex cis-20d derived from SPO 12 was puri-

fied by column chromatography (64%) and obtained as

a bright yellow solid (Scheme 7). Upon recrystallization from

petroleum ether and diethyl ether, suitable crystals of meso-20d

were obtained for an X-ray analysis (Figure 9).⁴⁷Selected bond

lengths and angles are given in Table 5.

1.581 A), and [Mn(CO)₄{(Ph₂PO)₂H}] (1.551 A),⁴²but fit

41

˚

within the normal range of P-O single bond lengths.⁴³For

˚

instance, the P-O bond (1.613 A) of complex 24 is indeed

longer compared to the PdO bond (1.4819 A) of free

˚

secondary phosphine oxide ligand 6.⁴⁴

The most interesting structural feature of trans complexes

concerns the hydrogen bonding involving P-O-H groups,

which account for their stabilization. Previous observations

reported by Berry et al.^39aon the cis-[PtCl₂(Ph₂POH)₂]THF

complex showed an intramolecular hydrogen bond with a

˚

chlorine atom (OH---Cl = 2.148 A) and an intermolecular

(39) (a) Berry, D. E.; Beveridge, K. A.; Bushnell, G. W.; Dixon, K. R.

Can. J. Chem. Soc. 1985, 63, 2949. (b) Han, L. B.; Choi, N.; Tanaka, M.

Organometallics 1996, 15, 3259. (c) Van Leeuwen, P.; Roobeek, C. F.;

Orpen, A. G. Organometallics 1990, 9, 2179. (d) Fornies, J.; Gomez, J.;

Lalinde, E.; Moreno, M. T. Inorg. Chim. Acta 2003, 347, 145. (e) Browning,

C. S.; Farrar, D. H. J. Chem. Soc., Dalton Trans. 1995, 12, 2005.

(40) Cornock, M. C.; Gould, R. O.; Jones, L.; Stephenson, T. A. J.

Chem. Soc., Dalton Trans. 1977, 13, 1307.

(41) Cotton, F. A.; Falvello, L. R.; Tomas, M.; Gray, G. M.;

Kraihanzel, C. S. Inorg. Chim. Acta 1984, 82, 129.

(42) Fawzi, R.; Hiller, W.; Lorenz, I. P.; Mohyla, J.; Zeiher, C. J.

Organomet. Chem. 1984, 262, C43.

The achiral complex is essentially planar and displays

an inversion center; the short distance between the two

˚

oxygen atoms [O1 O2 (2.373 A)] suggested a strong and

3 3 3

(45) Stout, G. H.; Jensen, L. H. X-ray Structure Determination, a

Practical Guide, 2nd ed.; MacMillan: New York, 1968; p 303.

(46) Five diastereomeric dimer complexes could be expected from one

racemic SPO: (R*,R*)(R*,R*); (R*,R*)(S*,S*); (R*,R*)(S*,R*); (R*,

S*)(R*,S*); (R*,S*)(S*,R*).

(43) Corbridge, D. E. C. The Structural Chemistry of Phosphorus;

Elsevier: Amsterdam. 1974.

(44) Dornhaus, F.; Lerner, H.-W.; Bolte, M. Acta Crystallogr. Sect. E

(47) The crystallographic data for complex 20d (CCDC 771342) have

been deposited with the Cambridge Crystallographic Data Centre.

These data can be obtained free of charge at www.ccdc.ac.uk/data

\request/cif.

2005, 61, o657.

Article

Organometallics, Vol. 29, No. 17, 2010 3943

Table 4. NMR Spectral Data of Platinum Complexes

entry

R¹

R²

trans

cis

dimer

1

2

3

4

5

6

t-Bu

Cy

Me

Ph

i-Bu

t-Bu

Cy

Me

Ph

i-Bu

Ph

109.2 (J = 2409 Hz)^a

107.2 (J = 2482 Hz)^a

no

73.7 (J = 3970 Hz)^b

70.9 (J = 4066 Hz)^a

88.9 (J = 3960 Hz)^c

no

54.3 (J = 3884 Hz)^a

53.5 (J = 4002 Hz)^c

no

87.8 (J = 2493 Hz)^a

87.0 (J = 2491 Hz)^a

87.8 (J = 2492 Hz)^a

90.9 (J = 2557 Hz)^d

90.6 (J = 2557 Hz)^d

86.1-85.8 ^b

61.4 (J = 3982 Hz)^c

63.1 (J = 3982 Hz)^c

65.0 (J = 4000 Hz)^a

58.9 (J = 3961 Hz)^a

57.5 (J = 3938 Hz)^a

51.6 (J = 3939 Hz) ^c

50.5 (J = 3919 Hz) ^c

55.5 (J = 3953 Hz)^c

54.5 (J = 3928 Hz)^c

7^e

8

t-Bu*

Cy

Ph*

Ph

84.9 (J = 4008 Hz)^a

77.3 (J = 4007 Hz)^c

74.8 (J = 3984 Hz)^c

69.9 (J = 3985 Hz) ^b

68.9 (J = 3974 Hz)^b

75.9 (J = 4021 Hz)^c

74.8 (J = 4008 Hz^c

9

Me

Ph

10

i-Bu

no

^aCDCl₃. ^{b 31}P NMR of platinum complexes recorded on a reaction mixture using a C₆D₆capillary as external reference in THF. ^cIn DCM.

^dIn CH₃CN. ^eComplexes with (S)-(-)-tert-butylphenylphosphine oxide.

˚

Table 5. Selected Bonds Lengths [A] and Angles [deg] for meso-

20d with Estimated Standard Deviations in Parentheses

Pt1-Cl1

Pt1-Cl2

Pt-P1

2.436(2)

2.431(2)

2.233(2)

2.226(2)

1.549(6)

1.527(7)

1.792(11)

1.833(7)

P2-C13

1.839(12)

1.812(8)

82.16(8)

92.09(8)

174.86(8)

174.21(8)

92.81(8)

92.96(9)

P2-C19

Cl1-Pt1-Cl2

Cl1-Pt1-P1

Cl1-Pt1-P2

Cl2-Pt1-P1

Cl2-Pt1-P2

P1-Pt1-P2

Pt-P2

P1-O1

P2-O2

P1-C1

P1-C7

Hydrogen Bonds

2.373

O1 O2

3 3 3

2.5.2. Synthesis and X-ray Crystal Structure of Chiral [(R_P,

R_P),(R_P,R_P)]-21d. On mixing PtCl₂(cod) and (S)-(-)-tert-butyl-

phenylphosphine oxide (S)-(-)-11⁵¹in dichloromethane at room

temperature to prevent racemization, complex 21d type I

was formed as a 1:1 mixture of cis and trans isomers.¹⁶It is

worth noting that coordination of the chiral t-Bu(Ph)POH

to the metal proceeds with retention of configuration. On

treatment with triethylamine, dinuclear platinum complex

[(R_P,R_P),(R_P,R_P)]-21d was obtained and purified by column

chromatography (50% yield) without loss of configuration

on the phosphorus atom. Suitable crystals were obtained

for an X-ray analysis (Figure 10).⁵²Selected bond lengths

and angles are given in Table 6.

Figure 9. Molecular structure of meso-[(R*_P,S*_P),(R*_P,S*_P)]-

20d (PLUTO representation). Most of the hydrogen atoms are

omitted for clarity.

symmetrical H-O-H bonding.⁷The X-ray structure of the

cis-[Pt₂(μ-Cl)₂{(Ph₂PO)₂H}₂]^11bcomplex reported by Berga-

˚

mini et al. showed intramolecular hydrogen bonds (2.415 A)

comparable to our complex 20d. To our best knowledge, this

X-ray structure provided a rare example of bridged-chlorine

nonsymmetrical-PA bis-platinum complexes. They belong to

the class of negative-charge-assisted H-bonds [(-)CAHB]⁴⁸in

which the negative charge spreads out between two oxygen

This structure is similar to those observed for complex

meso-20d (Figure 9), but in this case complex 21d has

approximate C₂symmetry and the two O-P-P-O planes

are slightly distorted, as observed with two pincer dihedral

angle (O1-P1-P2-O2 and O3-P3-P4-O4) values of 9°

and -5°, respectively.

atoms (O-H O)^-. Accordingly, all P-O bonds lengths are

3 3 3

of similar values [in the range 1.527(7)-1.549(6) A]⁴³and signi-

˚

49

˚

ficantly longer compared to PdO distances [1.48-1.50 A].

The Cl(1)-Pt-P(2) and Cl(2)-Pt-P(1) bond angle values of

174.8° and 174.2°, respectively, showed a slight tetrahedral

distortion.

A small dissymmetry for this complex induced by different

strengths of the two hydrogen bonds was observed. Indeed,

The two platinum centers located in square-planar structures

˚

are separated by 3.669 A, andthePt-Cl bond length average of

2.4335 A is usual for a chlorine-bridged dinuclear complex

˚

the distance O3-O4 (2.189 A) is shorter compared to the

˚

O1-O2 distance (2.227 A). The distance between the two

chlorine atoms (3.085 A) was found shorter compared to the

without metal-metal interaction.⁵⁰The Pt-P bond length

average (2.2295 A) is consistent with the low trans influence

˚

one observed for complex 20d (3.198 A). Bond lengths Pt-Cl

of chlorine, and the observed pincer P-O---H---O-P “biden-

˚

(average ≈ 2.4 A) and Pt-P (average ≈ 2.3 A) are in accord

tate” ligand is in accord with analogous structures.^11b,39

with chlorine-bridged dinuclear platinum complexes. The

(48) Gilli, P.; Bertolasi, V.; Ferretti, V.; Gilli, G. J. Am. Chem. Soc.

1994, 116, 909.

(51) NMR analyses became easier by monitoring the reaction with

enantiopure 11. For the enantioselective synthesis of SPOs, see ref 28b.

(52) The crystallographic data for complex 21d (CCDC 771341) have

been deposited with the Cambridge Crystallographic Data Centre.

These data can be obtained free of charge at www.ccdc.ac.uk/data

\request/cif.

(49) (a)Annibale,G.;Bergamini,P.;Bertolasi,V.;Besco, E.;Cattabriga,

M.; Rossi, R. Inorg. Chim. Acta 2002, 333, 116. (b) Goodwin, N. J.;

Henderson, W.; Nicholson, B. K. Inorg. Chim. Acta 2002, 335, 113.

(50) The Pt-Pt bond length average determined for 66 error-free data

from CSD³⁸is equal to 2.633 A.

˚

3944 Organometallics, Vol. 29, No. 17, 2010

Achard et al.

˚

average (1.54 A) fits with the usual value range in complexes

featuring a P-O

O-P^7,11b,40-43pincer and for com-

H

3 3 3 3 3 3

plex 20d (Table 5).

An interesting feature of the X-ray structure of 30 is the

association of the cis complex with the triethylammonium

ion through hydrogen bonding (see packing in Figure 12).

Henderson et al. reported an X-ray structure of platinum

thiosalicylate [(PPh₃)₂Pt(SC₆H₄CO₂) HNEt₃]⁺[BPh₄]^-

3 3 3

that revealed hydrogen bonding between the NH proton

and the carbonyl group of the thiosalicylate ligand.⁵⁵In

1

solution, the H NMR spectrum of complex 30 revealed

resonances due to the dissociated triethylammonium cation.

It is now established that C-H O bonds determine

3 3 3

crystal packing especially if stronger hydrogen bonding is

not observed.^56,57

In complex 30, the two ions are bound by three different

hydrogen bonds: NH Cl,⁵⁸CH O, and CH Cl. The

3 3 3

cell unit (see packing in Figure 12) is composed of four cis

complexes and four [NHEt₃]⁺in which the [NHEt₃]⁺ion

interacts with three different Pt complexes. The first cis

complex binds to the triethylammonium ion with two

Figure 10. Molecular structure of [(R_P,R_P),(R_P,R_P)]-21d (PLUTO

representation). All hydrogen atoms are omitted for clarity.

CH O-P hydrogen bonds, the second one with a C-H

3 3 3

Cl-Pt hydrogen bond, and the third one with a N-H Cl-Pt

3 3 3

hydrogen bond interaction. The two chlorine atoms of the first

complex are involved in two intermolecular hydrogen bonds

with two different [NHEt₃]⁺.

˚

Table 6. Selected Bonds Lengths [A] and Angles [deg] for

Compound [(R_P,R_P),(R_P,R_P)]-21d with Estimated Standard

Deviations in Parentheses

Orpen et al. reported different types of M-Cl H hydro-

3 3 3

Pt1-Cl1

Pt1-Cl2

Pt2-Cl1

Pt2-Cl2

Pt1-P1

Pt1-P2

Pt2-P3

Pt2-P4

P1-O1

P2-O2

2.443(5)

2.424(2)

2.403(5)

2.285(2)

2.237(8)

2.283(5)

2.281(5)

2.245(2)

1.539(6)

1.499(4)

P3-O3

1.598(4)

1.663(6)

78.67(10)

82.27(10)

173.7(9)

92.17(10)

172.9(9)

94.10(11)

92.04(8)

92.37(9)

gen bonds for neutral and ionic chlorine, classified as “short”

˚

P4-O4

˚

(e2.52 A), intermediate (2.52-2.95 A), and long interactions

Cl1-Pt1-Cl2

Cl1-Pt2-Cl2

Cl1-Pt1-P2

Cl1-Pt2-P3

Cl2-Pt1-P1

Cl2-Pt1-P4

P1-Pt1-P2

P3-Pt2-P4

˚

(2.95-3.15 A) (values based on the sum of van der Waals

radii for H and Cl: 1.20 + 1.75 = 2.95 A).⁵⁹The C-H

˚

3 3 3

Cl-M bond interactions are well established and importantly

represent connections in supramolecular chemistry.^59,60The

Pt-Cl H-N distance between the proton of [NHEt₃]⁺and

the chlorine atom (2.299 A) highlights intermolecular bond

interactions as “strong” hydrogen bonds.

3 3 3

˚

Hydrogen Bonds

2.227 O3 O4

The shortness of the NH Cl-Pt bond in complex 30

3 3 3

O1 O2

3 3 3

2.189

(Table 7) presumably derives in part from the large negative

charge on the chlorine atom in this partially ionic bond invol-

ving the cationic nitrogen. This ionic bond character, in agree-

3 3 3

Cl(1)-Pt1-P(2) and Cl(2)-Pt1-P(1) bond angle values of

173.7° and 172.9° respectively (Table 6), showed a slightly

tetrahedral distortion.

˚

ment with the longer Pt-Cl(1) length observed (2.398 A)

˚

compared with Pt-Cl(2) (2.390 A), suggested that the chlorine

2.6. Preparation and X-ray Crystal Structure of Platinum

Complex 30. Attempts to prepare complex 28d from 28

according to the established procedure as described for

complex 21d proved to be unsuccessful; instead the new cis

complex 30 (δ 63.9 ppm, J_Pt-P= 3974 Hz) was obtained in

51% yield after purification on column chromatography

(Scheme 8). The structure of 30 resolved by X-ray analysis

showed unusual features.⁵³

atom is involved in a weaker CH Cl bond. Moreover, the

˚

distance between nitrogen and chlorine atoms (3.179 A) is in

3 3 3

61

˚

agreement with typical distances N Cl (2.91-3.52 A).

3 3 3

The CH Cl hydrogen bond is generally weak due to the

poor acidity of the hydrogen in saturated carbon atoms. Usually,

strong hydrogen bonding has been reported when chloride ions

3 3 3

(55) Henderson, W.; Nicholson, B. K. Inorg. Chim. Acta 2003, 346, 7.

(56) Desiraju, G. R. Crystal Engineering. The Design of Organic

Solids; Elsevier: Amsterdam, 1989; pp 142-164.

(57) Seiler, P.; Dunitz, J. D. Helv. Chim. Acta 1989, 72, 1125.

(58) (a) Dyer, P. W.; Gibson, V. C.; Jeffery, J. C. Polyhedron 1995, 14,

3095. (b) Bashall, A.; Bond, A. D.; Doyle, E. L.; Garcia, F.; Kidd, S.; Lawson,

G. T.; Parry, M. C.; McPartlin, M.; Woods, A. D.; Wright, D. S. Chem.;Eur. J.

2002, 8, 3377. (c) Glidewell, C.; Low, J. N.; Skakle, J. M. S.; Wardell, J. L. Acta

Crystallogr., Sect. C: Cryst. Struct. Commun. 2004, 60, O872–O875. (d)

Complex 30 (Figure 11) consists of a slightly distorted square-

planar structure centered on a platinum atom (Cl-Pt-P angle

˚

≈ 176°, Table 7). The Pt-C1 bond length average of 2.394(3) A

is slightly elongated compared to several complexes containing a

trans Cl-Pt-P fragment (typical values ranging from 2.333 to

˚

2.366 A). In contrast, the Pt-P bond length average of 2.222 A

is shorter compared with those in cis-PtCl₂L₂complexes (typical

~

Wojciechowska, J. K.; Kononowicz, K.; Sieron,L. J. Mol. Struct. 2009,934, 123.

values ranging from 2.241 to 2.262 A).⁵⁴The P-O bond length

˚

(59) Aullon, G.; Bellamy, D.; Brammer, L.; Bruton, E. A.; Orpen,

A. G. Chem. Commun. 1998, 6, 653.

(60) (a) Balamurugan, V.; Mukherjee, J.; Hundal, M. S.; Mukherjee,

R. J. Struct. Chem. (Engl. Transl.) 2007, 18, 133. (b) Aakeroy, C. B.;

Evans, T. A.; Seddon, K. R.; Palinko, I. New J. Chem. 1999, 23, 145. (c)

Thallapally, P. K.; Nangia, A. Cryst. Eng. Commun. 2001, 27, 1. (d) Favero,

L. B.; Giuliano, B. M.; Melandri, S.; Maris, A.; Ottaviani, P.; Velino, B.;

Caminati, W. J. Phys. Chem. A 2005, 109, 7402. (e) Calhorda, M. J. Chem.

Commun. 2000, 801.

(53) The crystallographic data for complexes 30 (CCDC 771343)

have been deposited with the Cambridge Crystallographic Data Centre.

These data can be obtained free of charge at www.ccdc.ac.uk/data\

request/cif.

(54) Bushnell, T. E.; Densmore, R. J.; Dixon, K. R.; Ralfs, A. C. Can.

J. Chem. 1983, 61, 1132.

Article

Organometallics, Vol. 29, No. 17, 2010 3945

Scheme 8. Synthesis of cis Platinum Complex 30

˚

Table 7. Selected Bonds Lengths [A] and Angles [deg] for Complex

30 with Estimated Standard Deviations in Parentheses

Pt1-Cl1

Pt1-Cl2

Pt-P1

2.398(3)

2.390(3)

2.222(3)

2.222(2)

1.542(8)

1.553(8)

1.798(18)

1.818(14)

1.813(15)

1.816(15)

N1-C17

1.473(17)

1.493(17)

1.485(17)

88.99(11)

89.02(11)

176.96(11)

176.35(11)

87.97(11)

94.01(11)

116.9(3)

N1-C19

N1-C21

Pt-P2

Cl1-Pt1-Cl2

Cl1-Pt1-P1

Cl1-Pt1-P2

Cl2-Pt1-P1

Cl2-Pt1-P2

P1-Pt1-P2

Pt1-P1-O1

Pt1-P2-O2

P1-O1

P2-O2

P1-C1

P1-C5

P2-C9

P2-C13

116.6(3)

Hydrogen Bonds

D-H

A

D-H

H

A

D

A

D-H

3 3 3

A

3 3 3

C19-H O1

0.970

0.972

0.971

0.910

2.718

2.517

2.790

2.299

3.515

3.476

3.685

3.179

2.396

139.83

169.28

153.75

167.77

3 3 3

C21-H O2

3 3 3

C17-H Cl2^a

3 3 3

N1-H Cl1^a

3 3 3

O1 O2

Figure 11. Molecular structure of complex 30 (PLUTO repre-

sentation). Most hydrogen atoms are omitted for clarity.

3 3 3

^aChlorine from a second molecule of the Pt complex.

are involved rather than covalently bonded chlorine.⁶²The

˚

distance of 3.685 A between C(17) Cl in complex 30 is typical

3 3 3

of such interactions.^60,63Intermolecular interactions of chlorine

bonded to a metal atom^62b,63awith a saturated carbon such

as C Cl-Pt (3.582-3.852 A)⁶⁴and C Cl-Pd (3.523-

˚

3 3 3

3.783 A)⁶⁵have been reported.

˚

The third kind of hydrogen bond, which involved a

C-H---O interaction,^61,66is well established.^62a,67These

interactions are not restricted to small molecules but have

(61) (a) Hamilton, W. C.; Ibers, J. C. Hydrogen Bonding in Solids; W.

A. Benjamin: New York, 1968; p 16. (b) Jeffrey, G. A.; Saenger, W.

Hydrogen Bonding in Biological Structures; Springer-Verlag, study ed.,

1994; p 29. (c) Gatti, C.; May, E.; Destro, R.; Cargnoni, F. J. Phys. Chem. A

2002, 106, 2707. (d) Glidewell, C.; Low, J. N.; Skakle, J. M. S.; Wardell, S.;

Wardell, J. L. Acta Crystallogr., Sect. B: Struct. Sci. 2005, 61, 227.

(62) (a) Taylor, R.; Kennard, O. J. Am. Chem. Soc. 1982, 104, 5063.

(b) Braga, D.; Draper, S. M.; Champeil, E.; Grepioni, F. J. Org. Chem. 1999,

573, 73.

(63) (a) Campos-Gaxiola, J. J.; Hopfl, H.; Parra-Hake, M. Inorg.

Chim. Acta 2008, 361, 248. (b) Suksangpanya, U.; Blake, A. J.; Cade, E. L.;

Hubberstey, P.; Parker, D. J.; Wilson, C. CrystEngComm 2004, 6, 159.

(c) Balamurugan, V.; Mukherjee, R. CrystEngComm. 2005, 7, 337.

(64) Guerrero, M.; Pons, J.; Parella, T.; Font-Bardia, M.; Calvet, T.;

Ros, J. Inorg. Chem. 2009, 48, 8736.

(65) (a) Moro, A. C.; Watanabe, F. W.; Ananias, S. R.; Mauro, A. E.;

Netto, A. V. G.; Lima, A. P. R.; Ferreira, J. G.; Santos, R. H. A. Inorg.

Chem. Commun. 2006, 9, 493. (b) Agostinho, M.; Banu, A.; Braunstein, P.;

Welter, R.; Morise, X. Acta Crystallogr., Sect. C: Cryst. Struct. Commun.

2006, C62, M81–M86.

(66) (a) Gu, Y. L.; Kar, T.; Scheiner, S. J. Am. Chem. Soc. 1999, 121,

9411. (b) Steiner, T. Chem. Commun. 1997, 727.

(67) (a) Desiraju, G. R. Acc. Chem. Res. 1991, 24, 290. (b) Reetz, M. T.;

H€utte, S.; Goddard, R. J. Am. Chem. Soc. 1993, 115, 9339. (c) Song, J.-S.;

Szalda, D. J.; Bullock, R. M. J. Am. Chem. Soc. 1996, 118, 11134. (d)

Pedireddi, V. R.; Chatterjee, S.; Ranganathan, A.; Rao, C. N. R. J. Am.

Chem. Soc. 1997, 119, 10867. (e) Desiraju, G. R. Science 1997, 278, 404. (f)

Harakas, G.; Vu, T.; Knobler, C. B.; Hawthorne, M. F. J. Am. Chem. Soc.

1998, 120, 6405. (g) Kuduva, S. S.; Craig, D. C.; Nangia, A.; Desiraju, G. R.

J. Am. Chem. Soc. 1999, 121, 1936.

Figure 12. View of packing for complex 30 and some bonding

interactions in the crystal structure. Only hydrogen atoms

involved in H bonding are represented, in yellow.

also been reported for biological systems such as pro-

teins,⁶⁸nucleic acids,⁶⁹and carbohydrates.⁷⁰Moreover,

(68) (a) Derewenda, Z. S.; Lee, L.; Derewenda, U. J. Mol. Biol. 1995,

252, 248. (b) Bella, J.; Berman, H. M. J. Mol. Biol. 1996, 264, 734. (c)

Musah, R. A.; Jensen, G. M.; Rosenfeld, R. J.; McRee, D. E.; Goodin, D. B.;

Bunte, S. W. J. Am. Chem. Soc. 1997, 119, 9083.

3946 Organometallics, Vol. 29, No. 17, 2010

Scheme 9. Proposed Pathway for the Formation of Dimer D^a

Achard et al.

^aSubstituents at phosphorus atoms are omitted for clarity.

these interactions can persist in liquid phase.⁷¹The inter-

˚

molecular CH O distance average (3.495 A) found in

3 3 3

structure 30 fits in the range of such interactions.^65a,72

2.7. Proposed Mechanism of the Dimer Formation. The

formation of the binuclear chloro-bridged complex D might

be explained by an associative/dissociative mechanism

(Scheme 9). This may involve an 18e dimer bridged inter-

mediate C followed by loss of a chloride anion to afford the

neutral 16e chloro-bridged product D.

As shown previously, the stereochemistry of the initial

complex depends on the bulkiness of attached groups on the

phosphorus atom. Bulky substituents such as t-Bu groups at

the phosphorus atom gave the stable thermodynamic trans

complex A, unreactive toward triethylamine. Less bulky

groups such as Me gave cis complexes A⁰, prone to form

complex B in the presence of base. Small and bulky groups at

the phosphorus atom, such as Ph/t-Bu and Ph/Cy, gave

either cis and trans complexes A⁰and A. This suggested a

trans to cis isomerization prior to the formation of complex

B. Then B might evolve to dimer D through intermediate C

stabilized by halogen-metal bond interactions. Surpris-

ingly, a bulkier group such as i-Bu at the phosphorus atom

compared to a small group such as Me did not allow the

formation of complex D. Indeed, treatment of A with NEt₃

afforded only an unusual complex, 30. In this case, apical

coordination sites at the metal center would be less accessible

due to the steric hindrance of the i-Bu groups (Figure 13).

In summary, the course of the reaction highly depended on

the steric hindrance at the phosphorus atom. Less bulky

Figure 13. Intermediate C platinum complexes.

groups such as Me, i-Pr, Cy, or Ph drive the reaction to the

dimer probably through “intermediate C”. Indeed, moder-

ately bulky groups (i-Bu) allow the reaction to give cis

complex B, which upon treatment with triethylamine re-

mains intact. This ruled out an unstable 14e intermediate by

dissociation of a chloride ligand and subsequent dimeriza-

tion to form D.

2.8. Synthesis of Complex Pt(K²-acetato){[(t-Bu)₂PO]₂H},

31. Previously we reported the synthesis of a new class of

platinum complexes, Pt(κ²-acetato){[RPhPO]₂H}, featuring

the unusual κ²-acetato ligand with interesting catalytic

applications.¹⁶We wished to extend this class of complexes

to the bulky SPO (t-Bu)₂P(O)H 6 with the aim of accessing

more promising catalysts.

Treatment of 24 with silver acetate in dry dichloromethane

as described for the synthesis of complex 5 did not provide

the desired κ²-(acetato) platinum complex, instead trans

PtCl₂complex 24 was totally recovered (Scheme 10). A simi-

lar behavior was observed with treatment of complex trans-

24 with NEt₃.

Treatment of PtCl₂with 2 equiv of (t-Bu)₂P(O)H 6 in

refluxing DCM for 20 h led to a mixture of various platinum

complexes (see spectrum in Figure 14a). ³¹P NMR of the

crude mixture (a) showed the presence of cis (101.7 ppm,

J_Pt-P=3952 Hz) and trans complexes 24 in a 15:1 molar

(69) (a) Auffinger, P.; Westhof, E. Biophys. J. 1996, 71, 940. (b)

Berger, I.; Egli, M.; Rich, A. Proc. Nat. Acad. Sci. U. S. A. 1996, 93,

12116. (c) Wahl, M. C.; Rao, S. T.; Sundaralingam, M. Nat. Struct. Biol.

1996, 3, 24. (d) Egli, M.; Gessner, R. V. Proc. Nat. Acad. Sci. U. S. A. 1995,

92, 180. (e) Metzger, S.; Lippert, B. J. Am. Chem. Soc. 1996, 118, 12467. (f)

Auffinger, P.; Westhof, E. J. Mol. Biol. 1997, 274, 54. (g) Sigel, R. K. O.;

Freisinger, E.; Metzger, S.; Lippert, B. J. Am. Chem. Soc. 1998, 120, 12000.

(70) (a) Steiner, T.; Saenger, W. J. Am. Chem. Soc. 1992, 114, 10146.

(b) Steiner, T.; Saenger, W. J. Am. Chem. Soc. 1993, 115, 4540. (c) Wahl,

M. C.; Sundaralingam, M. Trends Biochem. Sci. 1997, 22, 97.

(71) (a) Jedlovszky, P.; Turi, L. J. Phys. Chem. B 1997, 101, 5429.

(b) Mizuno, K.; Ochi, T.; Shindo, Y. J. Chem. Phys. 1998, 109, 9502.

(72) Desiraju, G. R. Acc. Chem. Res. 1996, 29, 441.

Article

Organometallics, Vol. 29, No. 17, 2010 3947

Figure 14. ³¹P NMR spectra of platinum species derived from platinum and (t-Bu)₂P(O)H .

Scheme 10. Synthesis of (K²-Acetato) Platinum Complex 31

ratio, respectively. Previously we have shown that prepara-

tion of only the trans complex was achieved from PtCl₂(cod)

in THF solution. Addition of AgOAc (2 equiv) to the crude

mixture afforded a brown-yellow solution. The ³¹P NMR

spectrum (Figure 14b) showed a complex mixture contain-

ing trans complex 24 and two new cis complexes at δ 87.9

(J_Pt-P= 3992 Hz) and 78.6 (J_Pt-P= 3665 Hz) in a 1.35:1:1.9

ratio, respectively.⁷³One of these complexes proved to be the

desired κ²-acetato complex 31 (see below). Trace amounts of

cis complex 24 and uncoordinated SPO 6 were also detected.

Trans complex 24, observed when the reaction is over, arises

presumably from cis to trans isomerization induced by a

small amount of free SPO.⁷⁴Attempted separations of

products by column chromatography on silica or Fluorisil

were unsuccessful.

Figure 15. Molecular structure of 31 (PLUTO representation).

confirmed the presence of the acetato group with a singlet at δ

1.95 ppm. High-resolution mass spectrometry data [C₁₉H₄₀O₄-

P₂Pt (M þ H)^þ: 578.2124] supported the monomeric structure

for complex 31. ³¹P NMR revealed that cis complex 31 (87.5

ppm, J = 3988 Hz) (Figure 14c) was also observed as a bypro-

duct when the reaction was conducted with PtCl₂(Figure 14b).

2.9. X-ray Structure of Complex Pt(K²-acetato){[(t-Bu)₂-

PO]₂H} 31. X-ray analysis showed unambiguously the mon-

omeric form of 31 and an acetate group in κ²-coordination

mode (Figure 15).⁷⁵The complex is essentially planar with an

approximate C₂symmetry; the short distance between the

At this stage, a protocol to the cis configuration that requi-

red inducing the formation of the desired κ²-acetato plati-

num complex 31 was achieved. Treatment of trans complex

24 with both AgOAc (2 equiv) and NEt₃(1 equiv) in DCM

at room temperature for 12 h afforded straightforwardly

κ²-acetato complex 31 (Scheme 10 and Figure 14c) with com-

plete conversion. Purification by column chromatography

˚

two oxygen atoms [O1 O2 (2.399 A)] suggested a strong

3 3 3

1

on silica afforded 31 (90%) as a red-orange solid. H NMR

and symmetrical O-H-O bonding. We previously reported

(75) The crystallographic data for complexes 31 (CCDC 771344)

have been deposited with the Cambridge Crystallographic Data Centre.

These data can be obtained free of charge at www.ccdc.ac.uk/data

\request/cif. We observed a cocrystallization between two molecules of

31 having slightly different bond lengths; see Supporting Information.

(73) The first cis species is complex 31, and the second one might be an

intermediate such as [{(R₁R₂PO)₂H}PtCl(η¹-OAc)].

(74) (a) Louw, W. J. Inorg. Chem. 1977, 16, 2147. (b) Roulet, R.;

Barbey, C. Helv. Chim. Acta 1973, 56, 2179.

3948 Organometallics, Vol. 29, No. 17, 2010

Achard et al.

˚

Table 8. Selected Bonds Lengths [A] and Angles [deg] for Com-

pound 31 with Estimated Standard Deviations in Parentheses

˚

was distilled from sodium and stored over 4 A molecular sieves.

CH₂Cl₂and CH₃CN were distilled from CaH₂. Light petroleum

ether refers to the fraction distilled at bp 40-60 °C. Thin-layer

chromatography was carried out on Merck silica gel 60 F254

and visualized under ultraviolet light (254 and 366 nm), or

through spraying with 5% phosphomolybdic acid in EtOH, or

by placing in iodine vapor. Flash chromatography was per-

formed with Merck silica gel 60 (230-400 mesh).

Pt1-O3

Pt1-O4

Pt-P1

2.170(3)

2.168(3)

2.241(3)

2.237(2)

1.543(8)

1.540(8)

1.857(18)

1.876(14)

1.884(15)

1.858(15)

O3-C17

1.256(17)

1.275(17)

1.485(17)

60.10(11)

118.19(11)

93.32(11)

116.97(3)

116.75(3)

93.32(11)

O4-C17

C17-C18

Pt-P2

O3-Pt1-O4

O3-C17-O4

P1-Pt1-P2

Pt1-P1-O1

Pt1-P2-O2

P1-Pt1-P2

P1-O1

P2-O2

P1-C1

P1-C5

P2-C9

P2-C13

Physical and Analytical Measurements. Melting points were

determined in a capillary tube with a Metler LP61 apparatus. IR

spectra were recorded on an IRTF Perking-Elmer 1700X spec-

trophotometer. ¹H, ¹³C, and ³¹P NMR spectra were recorded on

Bruker Advance DPX spectrometers operating at 200 and 300

MHz for ¹H. ¹³C and ³¹P nuclei were observed with ¹H decoupling.

Phosphoric acid (85%) was used as external reference for ³¹PNMR

spectra. Chemical shifts (δ) of ¹H and ¹³C spectra are reported in

ppm relative to CHCl₃(δ = 7.26 for ¹H and δ = 77.0 for ¹³C).

J values are given in Hz.

Hydrogen Bonds

D-H

A

D-H

H

A

D

A

D-H

3 3 3

A

3 3 3

C3-H O3

0.961

0.960

0.961

2.463

2.587

2.430

2.797

3.300

3.396

3.335

3.262

2.399

145.46

141.84

156.74

110.65

3 3 3

C7-H O3

3 3 3

C12-H O4

3 3 3

High-resolution mass spectra were recorded on a Thermo

Fisher Scientific LTQ-ORBITRAP. Elemental analyses were

performed in the Elemental Microanalysis department of the

C16-H O4

3 3 3

O1 O2

3 3 3

the X-ray structure of Pt(κ²-acetato){(t-BuPhPO)₂H}₂,

ꢀ

ꢀ ^

Faculte de Saint Jerome.

4.2. Synthesis and Characterization. 4.2.1. Secondary Phos-

phine Oxide. (()-Di-tert-butylphosphine Oxide (6). A solution

of diphenylphosphite (0.4 mL, 2.13 mmol) in dry Et₂O (5 mL)

was added dropwise to a 1.7 M solution of t-BuLi in pentane

(4 mL, 6.8 mmol) in dry Et₂O (20 mL) at -40 °C. The resulting mix-

ture was stirred for 1 h at -40 °C and for 21 h at room temperature.

HCl (1 N, 7 mL) was added to the brown solution cooled to 0 °C,

and the solution mixture was stirred for 15 min. Et₂O (15 mL) was

added, and the mixture was stirred at 0 °C for an additional 5 min.

The aqueous layer was acidified with 1 N HCl (20 mL) and extracted

with DCM (2 ꢀ 20 mL) and CHCl₃(20 mL). The combined organic

phases were dried over Na₂SO₄and concentrated under vacuum.

Purification by column chromatography (Et₂O/MeOH, 97:3) on

deactivated silica gel (20:80 H₂O/silica) afforded the desired

product contaminated with trace amounts of water. A DCM

solution of the product was stirred over molecular sieves. Upon

evaporation of the solvent, 242 mg (70%) of 6 was obtained as a

white solid. NMR data are in agreement with reported data.⁴⁴

³¹P{¹H} NMR (CDCl₃, 81 MHz): δ 67.5.

(()-Dicyclohexylphosphine Oxide (7). A solution of cyclohexyl

chloride (6.4 g, 54.2 mmol) in THF (40 mL) was added dropwise

to a suspension of Mg (1.31 g, 54.2 mmol) previously activated

with dibromoethane (1%) in THF (3 mL). The resulting mixture

was stirred for 3 h at reflux. Then a solution of diphenylphos-

phite (2.539 g, 10.8mmol)inTHF(10mL) was added dropwiseto

the Grignard solution (54.2 mmol) at -10 °C. The resulting

mixture was stirred for 1 h at -10 °C and for 24 h at room

temperature. The resulting brown solution cooled to 0 °C was

quenched by addition of 1 N HCl (20 mL) and after 15 min

diluted with Et₂O (30 mL). The aqueous layer was acidified with 1

N HCl (20 mL) and extracted with Et₂O (2 ꢀ 30 mL) and EtOAc

(20 mL). The combined organic phases were washed with 10%

aqueous NaHCO₃, dried over Na₂SO₄, and concentrated under

vacuum. Purification by column chromatography (Et₂O/MeOH,

97:3) on deactivated silica gel (20:80 H₂O/silica) afforded the

desired product contaminated with trace amounts of water. A

DCM solution of the product was stirred over molecular sieves.

Upon evaporation of the solvent 1.74 g (78%) of 7 was obtained

as a white solid. NMR data are in agreement with reported

data.^{20e,78 31}P{¹H} NMR (CDCl₃, 81 MHz): δ 50.6 ppm.

(()-Dimethylphosphine Oxide (9). This was prepared accord-

ing to a published procedure.^{25 31}P{¹H} NMR (CDCl₃, 81 MHz):

δ 23.4.

which showed intramolecular hydrogen bonds O-H

O

3 3 3

(2.391 A) comparable to complex 31 (Table 8).^16aTo the best

of our knowledge this X-ray structure provided the first

example of a κ²-acetato platinum complex with a highly

electron-rich bulky phosphinous acid ligand.⁷⁶Indeed, struc-

turally defined (κ²-acetato)platinum(II) complexes have

been described in two reports.^16,77Usually, these κ²-acetato

complexes are extremely uncommon due to their propensity

to form dimeric carboxylate-bridged complexes. Accord-

˚

ingly, P-O bond lengths (average ≈ 1.541 A) are in agree-

ment with single P-O bonds values. The C-O bond length

˚

of an acetato ligand (average ≈ 1.27 A), between single (1.43 A)

˚

and double C-O bond (1.22 A) length, is in full agreement with

a partial double-bond character (Figure 15).

3. Conclusion

Various SPO preligands with substituents of tunable

bulkiness have been prepared for coordination mode inves-

tigations. The balance between steric and electronic factors

determines the coordination mode of mono- and dinuclear

platinum complexes. Bulky and electron-rich SPOs reacted

with platinum salts to form trans complexes. In contrast, less

hindered PA ligands coordinate to the metal in a cis fashion.

In between these frontiers, mixtures of cis and trans com-

plexes are obtained. Dinuclear chloro-bridged complexes

were observed after treatment of cis mononuclear complexes

with NEt₃. An associative/dissociative-type mechanism has

been proposed on the basis of isolation of intermediate 30.

Rare monomeric κ²-acetato platinum(II) complex 31 with

symmetrical bulky SPO preligands is being tested as a

catalyst in cycloaddition reactions in our laboratories.

4. Experimental Section

4.1. General Procedures. All solvents were purified by stan-

˚

dard procedures. THF and Et₂O were predried over 4 A mole-

cular sieves and distilled from sodium/benzophenone. Toluene

(76) Interestingly, there are only two records for the structural motif

M[(t-Bu)₂PO]₂H: (a) Mononuclear palladium complex see: Leoni, P.;

Marchetti, F.; Pasquali, M. J. Organomet. Chem. 1993, 451, C25–C27.

(b) Dinuclear palladium complex: see ref ⁹d. (c) A new bulky monocular Pd

complex has recently been reported (see ref ^16c).

(()-Diisobutylphosphine Oxide (10). A solution of diphenyl-

phosphite (2 g, 8.54 mmol) in THF (20 mL) was added dropwise

(77) Moret, M. E.; Keller, S. F.; Slootweg, J. C.; Chen, P. Inorg.

Chem. 2009, 48, 6972.

(78) Meciarova, M.; Toma, S.; Loupy, A.; Horvath, B. Phosphorus,

Sulfur, Silicon Relat. Elem. 2008, 183, 21.

Article

Organometallics, Vol. 29, No. 17, 2010 3949

to a 2 M solution of i-BuMgCl in THF (29.16 mmol, 15 mL)

cooled at -10 °C. The resulting mixture was stirred for 1 h at

-10 °C, warmed to rt, and stirred for 21 h at room temperature.

The resulting brown solution was cooled to 0 °C, quenched by

addition of 1 N HCl (15 mL), and after 15 min diluted with Et₂O

(30 mL). The aqueous layer was diluted with 1 N HCl (20 mL)

and extracted with DCM (2 ꢀ 30 mL). The combined organic

phases were washed with 10% aqueous NaHCO₃, dried over

Na₂SO₄, and concentrated under vacuum to give a colorless oil.

Purification by column chromatography (Et₂O/MeOH, 97:3)

on deactivated silica gel (20:80 H₂O/silica) afforded the desired

product contaminated with trace amounts of water. A DCM

solution of the crude product was stirred over molecular sieves.

Upon evaporation of the solvent 690 mg (50%) of 10 was

obtained as a colorless oil. NMR data are in agreement with

reported data.^{79 31}P{¹H} NMR (CDCl₃, 81 MHz): δ 31.5.

(()-tert-Butylphenylphosphine Oxide (11). This was prepared

according to a published procedure.^{15a 31}P{¹H} NMR (CDCl₃,

81 MHz): δ 48.7.

(()-Cyclohexylphenylphosphine Oxide (12). A solution of

cyclohexyl chloride (3.2 g, 27 mmol) in THF (20 mL) was added

dropwise to a suspension of Mg (activated with few drop of

dibromoethane) (1.4 g, 27 mmol) in THF (5 mL). The resulting

mixture was stirred for 3 h at reflux and cooled to -10 °C, and

a solution of ethyl phenylphosphinate (2 g, 11.8 mmol) in THF

(5 mL) was added dropwise. The mixture was stirred for 1 h at

room temperature; then water (5 mL) and 1 N HCl (10 mL) were

added successively to the solution at 0 °C. Et₂O (15 mL) was

added, and the aqueous phase was extracted with Et₂O (2 ꢀ

20 mL) and AcOEt (2 ꢀ 20 mL). The combined organic phases

were washed with 10% aqueous NaHCO₃, dried over MgSO₄,

and concentrated under vacuum to give 2.06 g (84%) of 12 as a

colorless oil. NMR data are in agreement with reported data.^15a

³¹P{¹H} NMR (CDCl₃, 81 MHz): δ 37.6.

J

_C-P= 4.7 Hz, CHꢀ2), 132.8 (t, J_C-P= 5.0 Hz, CHꢀ2). ³¹P{¹H}

NMR (CDCl₃, 81 MHz): δ 87.8 (s þ d, J_P-Pt= 2495 Hz), 87.1 (s þ

d, J_P-Pt= 2490 Hz) ppm. IR ν_max(KBr): 3401(br, P-OH) 2945,

2897, 2866, 1474, 1459, 1435, 1365, 1186, 1101(P-O), 1014, 904,809,

746, 694, and 608 cm^-1. LRMS: m/z calcd for C₂₀H₃₄NO₂P₂Cl₂Pt

(M þ NH₄)^þ648.1071, found 648.1072. Anal. Calcd for C₂₀H₃₀-

O₂P₂Cl₂P₂: C 38.11, H 4.80. Found: C 38.03, H 4.93.

Complex (R_P*,S_P*)-21 crystallized from CH₂Cl₂(51 mg, 30%

yield), and the single-crystal X-ray analysis revealed the trans

meso structure. ³¹P{¹H} NMR (CDCl₃, 81 MHz): δ 87.8 (s þ d,

J = 2494 Hz). ¹H NMR (CDCl₃, 200 MHz): δ 1.20 (d, J_H-P

=

8.1 Hz, 4.5H), 1.24 (d, J_H-P= 8.1 Hz, 4.5H), 7.45-7.48 (m,

3H), 7.97-8.06 (m, 2H). ¹³C{¹H} NMR (CDCl₃, 75 MHz): δ

26.38, 26.41, 26.45 (CH₃ꢀ3), 39.8 (2ꢀC, d, J_C-P= 25 Hz), 128.8

(t, J_C-P= 5.2 Hz, CHꢀ2), 130.1 (d, J_C-P= 45 Hz, Cꢀ2), 131.6

(s, CH), 132.7 (t, J_C-P= 6.2 Hz, CHꢀ2). ³¹P{¹H} NMR

(CDCl₃, 81 MHz): δ 87.8 (s þ d, J_P-Pt= 2493 Hz) ppm.

[(R_P,R_P)(R_P,R_P)]-[(μ-Cl)Pt(tert-butylphenylphosphinito)(tert-

butylphosphinous)]₂(21d). A solution of PtCl₂(cod) (60 mg, 0.16

mmol) and (S)-(-)-tert-butylphenylphosphane oxide 12 (58 mg,

0.32 mmol) in DCM (3 mL) was stirred overnight at room

temperature. NEt₃(0.16 mmol, 23 μL) was added to the yellow

solution, and the resulting mixture was stirred for 6 h at rt and

then concentrated under vacuum. Upon purification by chroma-

tography (PE/Et₂O, 1:1) over a pad of Celite and silica gel, 40 mg

(53%) of the title compound was obtained as a white solid.

Crystals suitable for X-ray analysis were obtained from PE/

Et₂O (1:1). Mp: 257-259 °C. [R]_D=-148 (c 0.1, CHCl₃) at rt.

¹H NMR (CDCl₃, 400 MHz): δ 1.01 (d, J_H-P=16 Hz, 36H),

7.32-7.35 (m, 12H), 7.42-7.79 (m, 8H). ¹³C{¹H} NMR (CDCl₃,

100 MHz): δ 26.8 (s, CH₃), 39.1 (dd, J_C-195Pt=4.3 Hz J_C-P=55.6

Hz, C), 127.7 (t, J_C-P= 5.4Hz, CH), 130.4 (s, CH), 131.8 (t, J_C-P

= 4.8 Hz, CH), 135.0 (dd, J_C-P= 3.5 Hz J_C-P=71 Hz, C) ppm.

³¹P{¹H} NMR (CDCl₃, 161 MHz): δ 58.7 (J_P-Pt= 3934 Hz),

60.2 (J_P-Pt= 3955 Hz). IR ν_max(KBr): 3058(w), 2957(m),

2943(m), 2924(w), 2896(w), 2863(w), 1474(m), 1459(m), 1436(m),

1392(w), 1365(w), 1308(w), 1259(w), 1184(m), 1098(s), 1036(P-O,

(()-Methylphenylphosphine Oxide (13). This was synthesized

following a published procedure.^{51b 31}P{¹H} NMR (CDCl₃, 81

MHz): δ 21.3.

s), 775(s), 742(s), 694(s) cm^-1. HRMS: m/z calcd for C₂₀H₃₀

O₂P₂ClPt (M þ H)^þ595.1048, found 595.1049.

-

(()-Isobutylphenylphosphine Oxide (14). A solution of ethyl

phenylphosphinate (2 g, 11.8 mmol) in THF (20 mL) was added

dropwise to a cooled (-10 °C) 2 M solution of i-BuMgCl (3.2 g,

27 mmol) in THF (20 mL). The resulting mixture was stirred for

12 h at rt, cooled to 0 °C, and quenched by addition of water

(5 mL) and 1 N HCl (10 mL). The mixture was diluted with

Et₂O (15 mL), and the aqueous phase was extracted with Et₂O

(2 ꢀ20 mL) and AcOEt (2 ꢀ20 mL). The combined organic

phases were washed with 10% aqueous NaHCO₃, dried over

MgSO₄, and concentrated under vacuum to afford 1.49 g (71%)

of 14 as a colorless oil. ¹H NMR (d₆-acetone, 200 MHz): δ 1.01

(d, J_H-P= 6.7 Hz, 3H), 1.06 (d, J_H-P= 6.6 Hz, 3H), 1.83-1.94

(m, 2H), 1.98-2.17 (overlap with solvent pick, m, 1H), 6.36 (dd,

J = 2.8 J_H-P= 4.1 Hz, 0.5H), 7.52-7.56 (m, 3H), 7.69-7.80

(m, 2H), 8.66 (t, J_H-P= 3.6 Hz, 0.5H). ³¹P{¹H} NMR (CDCl₃,

81 MHz): δ 21.8.

[(μ-Cl)Pt(()(cyclohexylphenylphosphinito)(cyclohexypheny-

phosphinous)]₂(20d). A solution of PtCl₂(cod) (176 mg, 0.47

mmol) and cyclohexylphenylphosphane oxide 12 (200 mg, 0.96

mmol) in DCM (10 mL) was heated at 40 °C for 4 h. NEt₃(0.47

mmol, 67 μL) was added to the yellow solution, and the resulting

mixture was stirred for 6 h at rt then concentrated under vacuum.

Uponpurification by chromatography (PE/Et₂O, 1:1)over a pad

of Celite and silica gel, 195 mg (65%) of the title compound was

obtained as a white solid as a 1:1 mixture of meso and dl isomers.

Mp: 161-164 °C. ¹H NMR (CDCl₃, 200 MHz): δ 1.75-2.26 (m,

44H), 7.18-7.30 (m, overlap with solvent peak), 7.42-7.52 (m,

3H). ¹³C{¹H} NMR (CDCl₃, 75 MHz): δ 25.9-26.1 (m, CH₂),

26.8 (s, CH₂), 26.9 (s, CH₂), 27.2-27.8 (m, CH₂), 28.6-28.8 (m,

CH₂), 39.7-41.6 (m, CH), 128.7-129.1 (m, CH), 130.7-131.0

(m, CH), 131.2-131.9 (m, CH), 135.2-136.8 (m, C) ppm. ³¹P-

{¹H} NMR(acetone-d₆, 81MHz): δ 58.7 (J_P-Pt= 3934 Hz), 60.2

(J_P-Pt= 3955 Hz). IR ν_max(KBr) 3445(P-OH, br), 2929(s),

2848(s), 1482(w), 1447(m), 1435(m), 1291(w), 1261(m), 1174(w),

1104(s), 1072(m), 1043(s), 1025(P-O, s), 915(w), 887(w), 801(s),

726(m), 693(s) cm^-1. HRMS: m/z calcd for C₂₄H₃₃O₂P₂ClPt

(M - H)^-647.1362, found 647.1363. Anal. Calcd for C₄₈H₆₆-

O₄P₄Cl₂Pt₂: C 44.62, H 5.15. Found: C 44.31, H 5.74.

4.2.2. Platinum Complexes. Dichlorobis[(()-tert-butylphenyl-

phosphinous acid]₂platinum(II) (21). A solution of PtCl₂(cod) (102

mg, 0.274 mmol) and (()-tert-butylphenylphosphine oxide (100

mg, 0.548 mmol) was stirred under refluxing THF (15 mL). After

24 h, the yellow solution was filtered over Celite and concentrated

under reduced pressure to afford quantitatively 21 as a yellow

powder. The ³¹P NMR spectrum shows two singlets at δ = 87.7

1

and 87.1, in a 1:1.1 meso/dl ratio. Mp: 227-230 °C. H NMR

(CDCl₃, 200 MHz): δ 1.20 (d, J_H-P= 8.1 Hz, 4.5H), 1.24 (d,

Recrystallization of complex 20d (PE/Et₂O, 1:1) gave suitable

microcrystals for X-ray analysis, which revealed a cis meso di-

meric structure, (R*_P,S*_P)(S*_P,R*_P)-20d. However, the minute

quantities ofmicrocrystalsdid notallowed a fullcharacterization.

Dichlorobis[di-tert-butylphosphinous acid]₂platinum(II) (24).

A solution of PtCl₂(cod) (115 mg, 0.308 mmol) and (()-di-

tert-butylphosphine oxide (100 mg, 0.612 mmol) was stirred

under refluxing THF (15 mL). After 16 h, the yellow solution

was filtered through a short pad of Celite and concentrated

J

_H-P= 8.1 Hz, 4.5H) this look like a triplet 9H, 7.45-7.48 (m,

3H), 7.97-8.06 (m,2H) ppm. ¹³C{¹H} NMR (CDCl₃, 75 MHz): δ

27.5 (CH₃ꢀ6), 28.1 (CH₃ꢀ6) 39.8 (2ꢀC, J_C-P= 26 Hz), 40-4

(2ꢀC, J_C-P= 18 Hz), 128.8 (t, J_C-P= 5.2 Hz, CHꢀ8), 129.1

(4ꢀC, J_C-P= 12 Hz), 129.9 (d, J_C-P= 40 Hz, Cꢀ2), 130.0 (d,

J_C-P= 46 Hz, Cꢀ2), 131.0 (s, 2ꢀCH), 131.1 (s, 2ꢀCH), 132.1 (t,

(79) Klaui, W.; Song, C. E. Inorg. Chem. 1989, 28, 3845.

3950 Organometallics, Vol. 29, No. 17, 2010

Achard et al.

under vacuum to afford quantitatively 24 as a yellow powder.

Complex 24 was crystallized by slow evaporation in CH₂Cl₂,

and the X-ray analysis of the monocrystal revealed the trans

configuration structure. Mp: 205-208 °C. ¹H NMR (CDCl₃, 200

MHz): δ 1.37 (d, J_H-P= 7.4 Hz, 18H), 1.41 (d, J_H-P= 7.3 Hz,

concentrated under vacuum. Upon purification by chromatogra-

phy (PE/Et₂O, 1:1) over a pad of Celite and silca gel, 84 mg (51%)

of the title compound was obtained as a yellowish solid. Mp:

105-110 °C. ³¹P{¹H} NMR (CDCl₃, 81 MHz): δ 63.9 (J_P-Pt

=

3974 Hz). IR ν_max(KBr): 3426 (P-OH, br), 2954(s), 2926(s),

2969(m), 1735(w), 1725(w), 1464(m), 1401(w), 1381(w), 1366(w),

1262(w), 1165(w), 1089(s), 1078(s), 1025(P-O, s), 848(w), 812(w),

and 754(w) cm^-1. HRMS:m/zcalcd for C₁₆H₃₇O₂P₂ClPt [M þ H]^þ

- [(HNEt₃)^þ- (Cl)^-] 554.1599, found 555.1657; [HNEt₃]^þwas

also observed at 102.1. When the sample was passed in negative

mode, C₁₆H₃₇O₂P₂Cl₂Pt (589.1284) was observed. Anal. Calcd for

C₂₂H₅₃NO₂P₂Cl₂Pt: C 38.21, H 7.72. Found: C 38.51, H 7.53.

In solution this compound was unstable, affording after a few

hours a mixture of two complexes: ammonium-free 30 and a

18H). ¹³C{¹H} NMR (CDCl₃, 50 MHz): δ major 28.7 (t, J_C-P

=

J_C-195Pt= 2.7 Hz, CH₃), minor 28.9 (t, J_C-P= J_C-195Pt= 2.7 Hz,

CH₃), major 39.6-40.0 (m, C), minor 41.9-42.1 (m, C). ³¹P{¹H}

NMR (CDCl₃, 81 MHz): δ 109.4 (s þ d, J_P-Pt= 2410 Hz). IR

ν_max(KBr): 3221 (P-OH, br), 2967, 2948, 1473, 1389, 1368, 1143

(P-O,s), 1022, 864, 811, 636 cm^-1. LRMS: m/z calcd for C₁₆H₃₇-

O₂P₂Cl₂Pt (M - H)^-589.1284, found 589.1287. Anal. Calcd for

C₁₆H₃₈O₂P₂Cl₂Pt₂: C 32.55, H 6.49. Found: C 32.71, H 6.43.

Dichlorobis[dicyclohexylphosphinous acid]₂platinum(II) (25).

A solution of PtCl₂(cod) (87 mg, 0.233 mmol) and (()-dicyclo-

hexylphosphine oxide (100 mg, 0.467 mmol) was stirred under

refluxing THF (15 mL). After 24 h, the yellow solution was

filtered through a short pad of Celite and concentrated under

vacuum to afford quantitatively 25 as a yellow powder. Com-

plex 25 crystallized from a CH₂Cl₂solution, and the X-ray

analysis of the monocrystal revealed the trans configuration

minor, unidentified complex (³¹P NMR δ 66.8 ppm (J_P-Pt

=

3927 Hz), ¹³C NMR spectra exhibit too many signals and are

uninformative for structural assignment).

K²-Acetato{[di-tert-butylphosphinito][di-tert-butylphosphinous

acid]}platinum(II) (31). NEt₃(85 μL, 0.616 mmol) and AgOAc

(205 mg, 1.23 mmol) were successively added to a solution of

complex 24 (426 mg, 0.616 mmol) in CH₂Cl₂(10 mL). The

resulting solution was stirred at room temperature for 20 h. The

solid residues were filtered over Celite, and the filtrate was

concentrated under vacuum. Flash chromatography over silica

gel (light petroleum/Et₂O, 1:1) afforded 305 mg (85%) of Pt

complex 31 as an orange powder. The formation of a single cis

complex, Pt(κ²-acetato){[(t-Bu)₂PO]₂H}, was confirmed by

³¹P{¹H} NMR (CDCl₃, 81 MHz): δ 87.6 (d; J_195Pt-P= 3990

Hz). Mp: 186-188 °C. ¹H NMR (CDCl₃, 200 MHz): δ 1.33 (d,

1

structure. Mp: 154-156 °C. H NMR (CDCl₃, 200 MHz): δ

1.25-2.16 (m, 46H). ¹³C{¹H} NMR (CDCl₃, 50 MHz): δ 26.2-

26.8 (m); 35.9-36.7 (m). ³¹P{¹H} NMR (CDCl₃, 81 MHz):

δ 107.2 (s þ d, J_P-Pt= 2485 Hz). IR ν_max(KBr): 3258 (br,

P-OH), 2927, 2852, 1447, 1273, 1162 (P-O), 1111, 1005, 891, 885,

863 cm^-1. LRMS: m/z calcd for C₂₄H₄₆O₂P₂Cl₂Pt (M - H)^-

693.1914, found 693.1908. Anal. Calcd for C₂₄H₄₆O₂P₂Cl₂Pt: C

41.50, H 6.68. Found: C 41.48, H 6.85. Due to the presence of the

cyclohexyl group within the structure, probably responsible for

dynamic conformational processes, ¹H and ¹³C NMR spectra

exhibit very broad signals and are uninformative for the structure

assignment.

J

_H-P= 14.4 Hz, 36H), 1.93 (s, 3H). ¹³C{¹H} NMR (CDCl₃, 50

MHz): δ 26.5 (CH₃), 28.6, 28.8, and 28.9 (CH₃ꢀ12), 39.4, 39.5,

39.9, 40.3, and 40.4 (CHꢀ4), 192.4 (CdO). IR (KBr): 2949,

2899, 2869, 1582, 1474, 1466, 1389, 1368, 1333, 1185, 1033, 1019,

993, 944, 898, 813, 689, 631 cm^-1. HRMS: m/z calcd for C₁₉H₄₀-

O₄P₂Pt (M þ H)^þ578.2117, found 578.2124; calcd for C₁₆H₃₇-

O₂P₂Pt (M - CH₃COO)^þ518.1909, found 518.1913.

Dichlorobis[dimethylphosphinous acid]₂platinum(II) (27). A

solution of PtCl₂(cod) (120 mg, 0.32 mmol) and (()-dimethyl-

phosphine oxide (50 mg, 0.64 mmol) was stirred under refluxing

THF (10 mL) for 22 h. The light yellow solution was filtered

through a short pad of Celite and concentrated under vacuum to

afford quantitatively 27 as a yellowish powder. The ³¹P NMR

spectrum showed one singlet at δ = 76.7 assigned to the cis

isomer. ¹H NMR (THF-d₈, 200 MHz): δ 2.03 (m, 12H). ³¹P{¹H}

NMR (THF-d₈, 81 MHz): δ 74.7 (sþd, J_P-Pt=3911 Hz). LRMS:

m/z calcd for C₄H₁₃O₂P₂Cl₂Pt (M - H)^-420.9401, found

420.9398.

Acknowledgment. We are grateful to CNRS and ANR

project “SPOs preligands” (Contract No. BLAN07-1_

190839) for financial support. We thank Dr. Michel Giorgi

ꢀ

(Universite P. Cezanne, Marseille) for his kind assis-

tance with X-ray analyses of complexes described in

this publication.

Dichloro[(di-isobutylphosphinito)(di-isobutylphosphinous)]-

platinum(II), Triethylammonium Salts (30). A solution of PtCl₂-

(cod) (90 mg, 0.242 mmol) and di-isobutylphosphane oxide 10

(80 mg, 0.493 mmol) in DCM (5 mL) was stirred under reflux for

22 h. NEt₃(0.242 mmol, 35 μL) was added to the yellow solution,

and the resulting mixture was stirred for 4 h at rt and then

Supporting Information Available: Experimental procedures

and characterization data of all new compounds. Tables of

crystallographic data in cif format. Table of DFT calculations

and histograms of 8a and 8b. This material is available free of

charge via the Internet at http://pubs.acs.org.

Article Doi

Steric control in the synthesis of phosphinous acid-coordinated mono- and binuclear platinum(II) complexes

DOI: 10.1021/om100602j

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Article abstract of DOI:10.1021/om100602j

Full text of DOI:10.1021/om100602j

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