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Cis-(hydrido)hydrocarbylplatinum(IV) complexes as intermediates in the PtIIC bond breaking
__Journal
otOrgano.
metalliC
Chemistry ELSEVIER
Journal of Organometallic Chemistry 488 (1995) C 13-C 14
Preliminary Communication
Cis-(hydrido) hydrocarbylplatinum(IV) complexes as intermediates in the Pt"-C bond breaking Vincenzo De Felice a, Augusto De Renzi b, Achille Panunzi b,, , Diego Tesauro b b
a Facoltgt di Agraria, Universitgl del Molise, Via Tiberio 21 A, 86100 Campobasso, Italy . . . . . Dlparttmento dt Chtmwa, Universith di Napoli "Federico H" Via Mezzocannone 4, 80134 Napoli, Italy
Received 7 October 1994
Abstract
Platinum(IV) complexes containing a c&-hydridohydrocarbyl arrangement have been obtained selectively on reaction of halotrimethylsilanes with bis(hydrocarbyl)(N,N-chelate)platinum(II) complexes. Hydrocarbon reductive elimination can be observed subsequently in solution. Keywords." Platinum; Hydride; Oxidative addition; Reductive elimination
It is generally accepted [1] that the cleavage of the P t n - C bond by protic acids occurs by a mechanism involving the oxidative addition of the electrophile to the metal, followed by the reductive elimination of hydrocarbon. A kinetic study, consistent with this mechanism has been also reported [2]. To the best of our knowledge a six-coordinate PtW-hydridohydrocar byl intermediate has never been isolated, although s o m e examples of Pt w hydrido complexes have been described [3]. By reaction of SiMe3X (X = CI or Br) with [PtR 2 (dmphen)] (dmphen = 2,9-dimethyl-l,10-phenanthroline; R = Me, or 4-MeOC6H 4) in wet a c e t o n e / diethyl ether, fairly stable Pt tv complexes, formally deriving by H X oxidative addition [4], were isolated in good yield as white precipitates. Generally, the water content in the reagent-grade commercial solvents was sufficient to ensure complete hydrolysis of the halosilanes, yielding electrophilic HX. [PtR2(dmphen)] + SiMe3X + H 2 0 = [ P t ( H ) X R 2 ( d m p h e n ) ] + SiMe3OH
~' Dedicated to Prof. Fausto Calderazzo in recognition of his prominent contribution to the advancement of organometallic chemistry. * Corresponding author. 0022-328X/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0 0 2 2 - 3 2 8 X ( 9 4 ) 0 0 0 3 8 - 7
The presence of a P t - H bond in the products is indicated by a medium absorption band in the IR spectrum at ca. 2300 cm -1, and a singlet in the 1H NMR spectrum at ca. - 2 2 6 (JPtH ca. 1400 Hz). In principle, four different stereochemical arrangements are possible, as indicated below for [Pt(H)XMe2(dmphen)] (X = C1 or Br; 1, 2). H
Me
Me
Me
t~Me X
Me
H
×
I
II
Ill
IV
The type I structure is commonly observed [5] as the result of a trans addition in the reaction of electrophiles to cis-[PtR2L2]. In our case, however, the non-equivalence of the two halves of the symmetric dmphen and of the two Pt-bound methyl groups in the ~H N M R spectrum rules out this geometry, as well as II. The large value of the P t - H coupling constant for the hydride is considered diagnostic [3b] for a hydride trans to a pttV-bound nitrogen, favours structure IV over structure IIl. This stereochemical arrangement could be a consequence of the steric demands of the dmphen [6]. The 1H N M R spectrum of the mother liquor when the solvent was acetone-d 6 showed no evidence for plat-
C14
V.. De Felice et al. /Journal of Organometallic Chemistry 488 (1995) C13-Cl4
i n u m h y d r i d e species o t h e r t h a n the p r e c i p i t a t e d p r o d uct. C o m p l e x e s 1 a n d 2 a r e stable in t h e solid state, b u t a r e d u c t i v e e l i m i n a t i o n p r o c e s s c o m p l e t e a f t e r 2 h, t a k e s p l a c e in c h l o r o f o r m solution. [Pt(H)XMe2(dmphen)]
= [PtXMe(dmphen)]
+ CH 4
The arylhydrido complex [Pt(H)CI(4-MeOC 6 H 4 ) 2 ( d m p h e n ) ] (3) was i s o l a t e d only in t h e solid state. Its d e c o m p o s i t i o n in solution, to [PtCI(4M e O C 6 H 4 ) ( d m p h e n ) ] a n d anisole, was f a s t e r t h a n t h a t o f the m e t h y l derivatives, thus p r e v e n t i n g c o m p l e t e c h a r a c t e r i z a t i o n by ~H N M R s p e c t r o s c o p y . F u r t h e r s t u d i e s on t h e reactivity o f t h e s e h y d r i d o species a r e c u r r e n t l y in p r o g r e s s .
1. Experimental details 1.1. General synthetic procedure
T o a s u s p e n s i o n of r e d [ P t R 2 ( d m p h e n ) ] [7] (0.1 m m o l ) in 2 ml o f 1 : 1 d i e t h y l e t h e r / a c e t o n e , M e 3 S i X was a d d e d in a slight excess ( 1 . 1 : 1 ratio) at r o o m t e m p e r a t u r e . A f t e r 0.5 h stirring, a white solid was s e p a r a t e d by filtration, w a s h e d twice with diethyl ether, a n d dried. Y i e l d s w e r e 5 0 - 6 0 % [8]. 1.2. R e d u c t i v e elimination
A 5 m g s a m p l e o f t h e h y d r i d o c o m p l e x was dissolved in 0.5 ml o f CDC13. T h e r e d u c t i v e e l i m i n a t i o n o f t h e h y d r o c a r b o n was m o n i t o r e d by I H N M R spectroscopy. A d d i t i o n o f diethyl e t h e r a f t e r t h e r e a c t i o n was comp l e t e d c a u s e d c r y s t a l l i z a t i o n o f yellow [ P t X R ( d m p h e n ) ] [9] in q u a n t i t i v e yield.
Acknowlegments W e t h a n k t h e Consiglio N a z i o n a l e delle R i c e r c h e a n d t h e M . U . R . S . T . for financial s u p p o r t , a n d the C e n t r o I n t e r d i p a r t i m e n t a l e di M e t o d o l o g i e C h i m i c o -
Fisiche, Universit?t di N a p o l i , for t h e use o f a B r u k e r AC-270 NMR spectrometer.
References and notes [1] J.P. Collmann, L.S. Hegedus, J.R. Norton and R.C. Finke, Principles and Applications of Organotransition Metal Chemistry, University Science Book, Mill Valley, C.A. 1987, Ch. 8, p. 439. [2] U. Belluco, M. Giustiniani and M. Graziani, J. Am. Chem. Soc., 89 (1967) 6494. [3] (a) J.E. Bentham, S. Cradock and E.A.V. Ebsworth, J. Chem. Soc., (A) (1971) 587; (b) I.C.M. Wehman-Ooyevaar, D.M. Grove, P. de Vaal, A. Dedieu and G. Van Koten, Inorg. Chem., 31 (1992) 5484. [4] V. De Felice, A. De Renzi, F. Ruffo and D. Tesauro, Inorg. Chim. Acta, 219 (1994) 169. [5] P.K. Monaghan and R.J. Puddephatt, J. Chem. Soc., Dalton Trans., (1988) 595. [6] V.G. Albano, G. Natile and A. Panunzi, Coord. Chem. Rev., 133 (1994) 67. [7] [PtR2(dmphen)] were prepared by adapting described procedures. P.K. Monaghan and R.J. Puddephatt, Organometallics, 3 (1984), 444; M.E. Cucciolito, V. De Felice, A. Panunzi and A. Vitagliano, Organometallics, 8 (1989) 1180. 1H NMR data for [PtMeE(dmphen)] ((CD3)2CO) 8 ppm: 8.52 (d, 2H), 7.87 (s, 2H), 7.70 (d, 2H), 2.96 (s, 6H, 2 Me), 1.06 (s, 2Jpt H = 80 H z , 6H, Pt-Me); [Pt(4-MeOC6H4)2(dmphen)] (CDC13) 6 ppm: 8.28 (d, 2H), 7.80 (s, 2H), 7.47 (d, 2H), 7.29 (d, 3Jptn = 74 Hz, 4H, 4 At-H), 6.55 (d, 4H, 4 Ar-H), 3.69 (s, 6H, 20Me), 2.20 (s, 6H, 2 Me). [8] Selected physical and spectroscopic data. 1: IR (Nujol): 2300 cm -1 (u Pt-H). 1H NMR data (CDCI 3) 8 ppm: 8.32 (d, 1H), 8.30 (d, 1H), 7.84 (s, 2H), 7.80 (d, 1H), 7.64 (d, IH), 3.19 (s, 2 Me), 1.64 (s, Pt-Meeq , 2JptH = 71 Hz, 3H), 0.52 (s, Pt-Mea~, 2Jpt H = 71 Hz, 3H), - 22.10 (s, Pt-H, 1Jpt H = 1404 Hz, 1H). Elemental Anal. Found: C, 40.95; H, 4.00; N, 5.85. C16HwC1NzPt, Calc.: C, 40.90; H, 4.07; N, 5.96%. 2: IR (Nujol): 2300 cm -1 (uPt-H). IH NMR data (CDC13) ppm: 8.32 (d, 1H), 8.30 (d, 1H), 7.84 (s, 2H), 7.78 (d, 1H), 7.66 (d, 1H), 3.20 (s, 6H, 2 Me), 1.69 (s, Pt-Meeq, 2Jpt H = 70 H z , 3H), 0.57 (s, Pt-Meax, 2Jpt_ H = 71 Hz, 3H), -21.88 (s, Pt-H, IJpt H = 1350 Hz, 1H). Elemental Anal. Found: C, 37.50; H, 3.85; N, 5.35. C16H19BrN2Pt, Calc.: C, 37.36; H, 3.72; N, 5.45%. 3: IR (Nujol): 2290 cm - l (uPt-H). Elemental Anal. Found: C, 47.30; H, 4.20; N, 4.80. C2zH23CINzOPt, Calc.: C, 47.02; H, 4.12; N, 4.98%. [9] The compounds were identified by comparison with independently synthesized samples V. De Felice, A. De Renzi, D. Tesauro and A. Vitagliano, Organometallics, 11 (1992) 3669.
otOrgano.
metalliC
Chemistry ELSEVIER
Journal of Organometallic Chemistry 488 (1995) C 13-C 14
Preliminary Communication
Cis-(hydrido) hydrocarbylplatinum(IV) complexes as intermediates in the Pt"-C bond breaking Vincenzo De Felice a, Augusto De Renzi b, Achille Panunzi b,, , Diego Tesauro b b
a Facoltgt di Agraria, Universitgl del Molise, Via Tiberio 21 A, 86100 Campobasso, Italy . . . . . Dlparttmento dt Chtmwa, Universith di Napoli "Federico H" Via Mezzocannone 4, 80134 Napoli, Italy
Received 7 October 1994
Abstract
Platinum(IV) complexes containing a c&-hydridohydrocarbyl arrangement have been obtained selectively on reaction of halotrimethylsilanes with bis(hydrocarbyl)(N,N-chelate)platinum(II) complexes. Hydrocarbon reductive elimination can be observed subsequently in solution. Keywords." Platinum; Hydride; Oxidative addition; Reductive elimination
It is generally accepted [1] that the cleavage of the P t n - C bond by protic acids occurs by a mechanism involving the oxidative addition of the electrophile to the metal, followed by the reductive elimination of hydrocarbon. A kinetic study, consistent with this mechanism has been also reported [2]. To the best of our knowledge a six-coordinate PtW-hydridohydrocar byl intermediate has never been isolated, although s o m e examples of Pt w hydrido complexes have been described [3]. By reaction of SiMe3X (X = CI or Br) with [PtR 2 (dmphen)] (dmphen = 2,9-dimethyl-l,10-phenanthroline; R = Me, or 4-MeOC6H 4) in wet a c e t o n e / diethyl ether, fairly stable Pt tv complexes, formally deriving by H X oxidative addition [4], were isolated in good yield as white precipitates. Generally, the water content in the reagent-grade commercial solvents was sufficient to ensure complete hydrolysis of the halosilanes, yielding electrophilic HX. [PtR2(dmphen)] + SiMe3X + H 2 0 = [ P t ( H ) X R 2 ( d m p h e n ) ] + SiMe3OH
~' Dedicated to Prof. Fausto Calderazzo in recognition of his prominent contribution to the advancement of organometallic chemistry. * Corresponding author. 0022-328X/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved SSDI 0 0 2 2 - 3 2 8 X ( 9 4 ) 0 0 0 3 8 - 7
The presence of a P t - H bond in the products is indicated by a medium absorption band in the IR spectrum at ca. 2300 cm -1, and a singlet in the 1H NMR spectrum at ca. - 2 2 6 (JPtH ca. 1400 Hz). In principle, four different stereochemical arrangements are possible, as indicated below for [Pt(H)XMe2(dmphen)] (X = C1 or Br; 1, 2). H
Me
Me
Me
t~Me X
Me
H
×
I
II
Ill
IV
The type I structure is commonly observed [5] as the result of a trans addition in the reaction of electrophiles to cis-[PtR2L2]. In our case, however, the non-equivalence of the two halves of the symmetric dmphen and of the two Pt-bound methyl groups in the ~H N M R spectrum rules out this geometry, as well as II. The large value of the P t - H coupling constant for the hydride is considered diagnostic [3b] for a hydride trans to a pttV-bound nitrogen, favours structure IV over structure IIl. This stereochemical arrangement could be a consequence of the steric demands of the dmphen [6]. The 1H N M R spectrum of the mother liquor when the solvent was acetone-d 6 showed no evidence for plat-
C14
V.. De Felice et al. /Journal of Organometallic Chemistry 488 (1995) C13-Cl4
i n u m h y d r i d e species o t h e r t h a n the p r e c i p i t a t e d p r o d uct. C o m p l e x e s 1 a n d 2 a r e stable in t h e solid state, b u t a r e d u c t i v e e l i m i n a t i o n p r o c e s s c o m p l e t e a f t e r 2 h, t a k e s p l a c e in c h l o r o f o r m solution. [Pt(H)XMe2(dmphen)]
= [PtXMe(dmphen)]
+ CH 4
The arylhydrido complex [Pt(H)CI(4-MeOC 6 H 4 ) 2 ( d m p h e n ) ] (3) was i s o l a t e d only in t h e solid state. Its d e c o m p o s i t i o n in solution, to [PtCI(4M e O C 6 H 4 ) ( d m p h e n ) ] a n d anisole, was f a s t e r t h a n t h a t o f the m e t h y l derivatives, thus p r e v e n t i n g c o m p l e t e c h a r a c t e r i z a t i o n by ~H N M R s p e c t r o s c o p y . F u r t h e r s t u d i e s on t h e reactivity o f t h e s e h y d r i d o species a r e c u r r e n t l y in p r o g r e s s .
1. Experimental details 1.1. General synthetic procedure
T o a s u s p e n s i o n of r e d [ P t R 2 ( d m p h e n ) ] [7] (0.1 m m o l ) in 2 ml o f 1 : 1 d i e t h y l e t h e r / a c e t o n e , M e 3 S i X was a d d e d in a slight excess ( 1 . 1 : 1 ratio) at r o o m t e m p e r a t u r e . A f t e r 0.5 h stirring, a white solid was s e p a r a t e d by filtration, w a s h e d twice with diethyl ether, a n d dried. Y i e l d s w e r e 5 0 - 6 0 % [8]. 1.2. R e d u c t i v e elimination
A 5 m g s a m p l e o f t h e h y d r i d o c o m p l e x was dissolved in 0.5 ml o f CDC13. T h e r e d u c t i v e e l i m i n a t i o n o f t h e h y d r o c a r b o n was m o n i t o r e d by I H N M R spectroscopy. A d d i t i o n o f diethyl e t h e r a f t e r t h e r e a c t i o n was comp l e t e d c a u s e d c r y s t a l l i z a t i o n o f yellow [ P t X R ( d m p h e n ) ] [9] in q u a n t i t i v e yield.
Acknowlegments W e t h a n k t h e Consiglio N a z i o n a l e delle R i c e r c h e a n d t h e M . U . R . S . T . for financial s u p p o r t , a n d the C e n t r o I n t e r d i p a r t i m e n t a l e di M e t o d o l o g i e C h i m i c o -
Fisiche, Universit?t di N a p o l i , for t h e use o f a B r u k e r AC-270 NMR spectrometer.
References and notes [1] J.P. Collmann, L.S. Hegedus, J.R. Norton and R.C. Finke, Principles and Applications of Organotransition Metal Chemistry, University Science Book, Mill Valley, C.A. 1987, Ch. 8, p. 439. [2] U. Belluco, M. Giustiniani and M. Graziani, J. Am. Chem. Soc., 89 (1967) 6494. [3] (a) J.E. Bentham, S. Cradock and E.A.V. Ebsworth, J. Chem. Soc., (A) (1971) 587; (b) I.C.M. Wehman-Ooyevaar, D.M. Grove, P. de Vaal, A. Dedieu and G. Van Koten, Inorg. Chem., 31 (1992) 5484. [4] V. De Felice, A. De Renzi, F. Ruffo and D. Tesauro, Inorg. Chim. Acta, 219 (1994) 169. [5] P.K. Monaghan and R.J. Puddephatt, J. Chem. Soc., Dalton Trans., (1988) 595. [6] V.G. Albano, G. Natile and A. Panunzi, Coord. Chem. Rev., 133 (1994) 67. [7] [PtR2(dmphen)] were prepared by adapting described procedures. P.K. Monaghan and R.J. Puddephatt, Organometallics, 3 (1984), 444; M.E. Cucciolito, V. De Felice, A. Panunzi and A. Vitagliano, Organometallics, 8 (1989) 1180. 1H NMR data for [PtMeE(dmphen)] ((CD3)2CO) 8 ppm: 8.52 (d, 2H), 7.87 (s, 2H), 7.70 (d, 2H), 2.96 (s, 6H, 2 Me), 1.06 (s, 2Jpt H = 80 H z , 6H, Pt-Me); [Pt(4-MeOC6H4)2(dmphen)] (CDC13) 6 ppm: 8.28 (d, 2H), 7.80 (s, 2H), 7.47 (d, 2H), 7.29 (d, 3Jptn = 74 Hz, 4H, 4 At-H), 6.55 (d, 4H, 4 Ar-H), 3.69 (s, 6H, 20Me), 2.20 (s, 6H, 2 Me). [8] Selected physical and spectroscopic data. 1: IR (Nujol): 2300 cm -1 (u Pt-H). 1H NMR data (CDCI 3) 8 ppm: 8.32 (d, 1H), 8.30 (d, 1H), 7.84 (s, 2H), 7.80 (d, 1H), 7.64 (d, IH), 3.19 (s, 2 Me), 1.64 (s, Pt-Meeq , 2JptH = 71 Hz, 3H), 0.52 (s, Pt-Mea~, 2Jpt H = 71 Hz, 3H), - 22.10 (s, Pt-H, 1Jpt H = 1404 Hz, 1H). Elemental Anal. Found: C, 40.95; H, 4.00; N, 5.85. C16HwC1NzPt, Calc.: C, 40.90; H, 4.07; N, 5.96%. 2: IR (Nujol): 2300 cm -1 (uPt-H). IH NMR data (CDC13) ppm: 8.32 (d, 1H), 8.30 (d, 1H), 7.84 (s, 2H), 7.78 (d, 1H), 7.66 (d, 1H), 3.20 (s, 6H, 2 Me), 1.69 (s, Pt-Meeq, 2Jpt H = 70 H z , 3H), 0.57 (s, Pt-Meax, 2Jpt_ H = 71 Hz, 3H), -21.88 (s, Pt-H, IJpt H = 1350 Hz, 1H). Elemental Anal. Found: C, 37.50; H, 3.85; N, 5.35. C16H19BrN2Pt, Calc.: C, 37.36; H, 3.72; N, 5.45%. 3: IR (Nujol): 2290 cm - l (uPt-H). Elemental Anal. Found: C, 47.30; H, 4.20; N, 4.80. C2zH23CINzOPt, Calc.: C, 47.02; H, 4.12; N, 4.98%. [9] The compounds were identified by comparison with independently synthesized samples V. De Felice, A. De Renzi, D. Tesauro and A. Vitagliano, Organometallics, 11 (1992) 3669.