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Platinum(O) compounds with triarylphosphine and analogous ligands
Platinum(O) compounds with triarylphosphine and analogous ligands LAMBERTO MALATESTA E CONCETTA CARIELLO I s t i t u t o di Chimiea~ Generlde d e l l ' U n l v e r s i t ~ dl Milano - I t a l i a
Summary: New p l a t i n u m deri,~ttives, l m v i n g oxichttion n u m b e r zero, w i t l t t r i a r y l phospldnes, trtarylarsine~, t r h w y i p h o s p l d t e s are described. Some of these eompoumh are c o o r d i n a t i v e l y ~ttttrated, i. e. of the t y p e Ptu(PAra)t, o t h e r are u n s a t u r a t e d , of t h e t y p e
Ptot PAr s)a. The p h o s p h i n e d e r i v a t i v e s r e a c t s w i t h c a r b o n m o n o x i d e g i v i n g m i x e d cnrbonyl-phosphine derivatives.
The analogies between palladium and platinum compounds of the same oxidation number, i. e. 2 and 4, are considerable. Consequently, after the preparation, by one of us [1], of stable palladium(O) compounds, it appeared likely that similar • zerovalent ,~ compounds of platinum might be obtained. Therefore we began this investigation and its preliminary results were communicated in a short note [2]. The tirst palladium(O) compounds, bis(arylisonitryl)paUadium(O), were prepared from the dialogenodiisonitrylpalladium(ll) and excess of isonitryl with ethanolic potassium hydroxide. From these diisonitrylpalladium(O) compounds the tetrakis(triarylphosphine)palladium(O) and tetrakis(triarylphosphite)palladium(O) were obtained. The same phosphine and phosphite derivatives were prepared successively, by direct reduction of palladium(I/) compounds. The dihaiogenobis(aD.lisonitryl)platinum(//) are well known and form two series of compounds considered as structural isomers:
[l'/x2(CNl~,).,.l
and
[Pt(CXI-O,] [PIN,]
The compounds of the former series are very similar to the dihalogenolfis(arylisonitryl)palladium(IIL from which bis(arylisonitryl)palladium(O) had been prepared. All our attempts to obtain the presumed isonitDqderivatives of platinum(O) were, however, unsuccessful. Although many reducing agents "16
5~
LAMBERTO MALATESTA~ CONCETTA CARIELLO
cause changes in the solution of these dialogenides without any separation of metallic platinum, no product could be isolated. On the other hand the attempts to obtain the platinum(O) compounds with tervalent phosphorus donors, from platinum(I/) derivatives, gave the expected result. The best reducing agent for this purpose appears to be an ethanolic solution of anhydrous hydrazine, which reacts with the dialogenobis(triphenylphosphine)platinum(ll), or with the dihalogenobis(triphenylphosphite)platinum(II) and excess ligana as follows: PlI,(PR~)~ + 2,5 HtNNHt + 2 PR, =: Pl(PRs), + ~/s N, + 2 HsNNH3I forming the tetrakis(triphenylphosphine)platinum(O) and the tetrakis(triphenylphosphite)platinum(O), strictly analogous to the corresponding palladium(O) compounds. The triphenylphosphine derivative is yellow, crystalline, soluble in benzene and chloroform, almost insoluble in ethanol, and stable to air for many hours. The triphenylphosphite derivative, white and more soluble in ethanol, is quite similar. The cryoscopic determinations in benzene of both products show a dissociation which increases with time. The phosphine derivatives (as it is the analogous with palladium) can also be obtained both from dihalogenobis(triphenylphosphine)platinum(I/), triphenylphosphine and ethanolic potassium hydroxide or from chloroplatinate(I/) triphenylphosphine and ethanolic potassium hydroxide. The reduction could be due to phosphine: PIX,,(PRs), + 3 PR8 + KOH = PI(PR3), + POR8 + 2 K X + H~O or to the potassium ethoxide. This method cannot, of course, be used for the preparation of the phosphite derivative, in account of hydrolysis. The tetrakis(triphenylphosphite)platinum(O) can be obtained from the phosphine derivatives by ligand exchange: Pt(PR,), + 4 P(0R), = P t l P ( 0 R ) d , + 4 PRs
"Platinum appears to form these zerovalent compounds more readily than palladium, since, while the dihalogenobis(triphenylphosphine)palladium(I/) reacts with hydrazine (without excess of ligand) giving metal-
PT(O) COMPOI.YNDS WITH THIARYLPHOSPHINE
AND ANALOGOUS I.IGANDS
563
lic palladium, the dihalogenobis(triphenylphosphine)platinum(II) dispropotionates forming an unsaturated platinum(0) compound:
-i PtI,(PR~)2 + H.NNH, = 2 Pt(PRs), + Pt,ls (PRJ,(NH2NH,) + + 2N~ + 4 H I
The tris(triphenyl)platinum(0) is yellow, crystalline, stable to air. If this compound is monomeric, as it is probable, it must be a planar molecule, with s p* hybrid orbitals: while the PI (PR,), are almost certainly tetrahedral with s p* hybrid orbitals, as tetracarbonylnichel. Tris(triphenylphosphine)platinum(0), though coordinatively unsaturated, appears to be dissociated in benzene solution. This dissociation might be due to a replacement of the phosphine by a molecule of solvent Pt(PR3)~ + CsH.-----Pt (PRs)sC,Hs ÷ PRa.
A product, having the approximate composition of Pt [P(C,HJ,l,,snCsHs was in fact isolated. The product written as Pt, I,(N,H4)(PR3) s is supposed t o be ~-hydrazinebis(diiodotriphenylphosphine)platinum(lI), but it could not be yet isolated in a pure state and the analysis of the impure product gave only a qualitative evidence. Also the dihalogenobis(triphenylphosphite)platinum(ll)reactswith hydrazine giving the tricoordinated platinum(0)-phosphite derivative, i. e. pto[P(OR)s]s, which is white, crystalline, stable to air and dissociated in benzene solution, All the above reactions when carried out with tris-p.chlorophenylphosphine instead of triphenytphosphine, give only the tricoordinate Pt°-derivative Pl[P(CICstl,)s]s, even when a great excess of ligand is used. It is noteworth that, with palladium too, the corrispondent tricoordinated compound is formed. The reaction between tris(p.chlorophenylphosphine)platinum(0) and triphenylphosphite in excess gives a product vdth three molecules of phosphite and one molecule of phosphine:
Ptl(CIC, H,hP]s + 3 (CeHsO)sP = Pt(CIC,HJ~P[(C,H60)sP]s + + 2 P(CICsH4)s while with the other phosphines these mixed products can be obtained only using the calculated amount of phosphite:
pIoI ( C, H s)sP], + 3 ( Cl CsH, O)sP = PP( CsHs)sP[( Cl C J t ,O hP ],, This behavour suggests that platinum(O) tends to give three equivalent bonds, different from the fourth. The latter, which has perhaps
564
LAMBERTO MALATESTA, CONCETTA CARIELLO
less 7~ charachter than the others is not strictly necessary to the stability of the compound itselfand need not be formed as in the three coordinated derivatives described above. This behavior finds a parallel in the halogenotetraisonitrylrhodium(1) compounds [3], which have a isonitryl group less than required by coordinative saturation (four instead of five), and often bind a molecule of solvent. The phosphine and phosphite platinum(O) compound to not bind alchool but in contact with chloroform, they exchange a part of the ligand (about 0,5 tool) with the solvent. The Pt°-compounds with arylarsines are analogous to the saturated ones with phosphines. They could be obtained only by reduction with hydrazine and an excess of ligand on the dihalogeno-bis(triarylarsine) platinum(If):
PtCI,(R,As,) + 2 R,As + */,H , N N H , = Pt(RaAs), + ~/,N, + 2 HCI They are very similar to, but much less stable than, the phosphine compounds of the same serie. The Pl(O)-derivativeswere reacted with carbon monoxide under pressure in an attempt to prepare platinum(O) derivatives analogous to those of nickel, which had been obtained by action of phosphines and phospites on tetracarbonylnickel [4]. W e found that the phosphite compounds do not react with carbon monoxide while the phosphine compound add two molecules of it. As the coordination number of platinum(O) cannot exceed four, one must assume that the following reactions have taken place:
Pt(a,P), + 2 c o = Pt(Co),(Pa,), + 2 Pa, PI(R,P), + 2 C O = PI(CO),(PR,), + PR,
The phosphine displaced by the carbon monoxide cannot be removed from the reaction mixture because, if one tries to dissolve it in a solvent it reacts with the product substituting one carbon monoxide molecule:
PI(CO)t(R,P), + PR, = Pt(CO)(R,P), + CO Tris(p.chlorophenylphosphine)platinum(O) after treatment with carbon monoxide first and then with diethylether gives the coordinatively unsaturated compound Pt(CO)[P(CICeH4)s], wich may be formed either by the action of the solvent on a primary product which is coordinatively saturated:
PI(CO),[(CIC,H.),P], = Pt(CO) [(CIC,H.)aP], + CO
PT(O) COMPOUNDS 'WITH TRIARYLPHOSPHINE AND ANALOGOUS LIGANDS
565
or by reaction of a coordinatively unsaturated primary product with the displaced phosphine: I't(CO),(ClC, II,)aP + (CICeH,)aP = Pl(CO)[(CICsH,)aP]., + CO These bicarbonylderivatives were not isolated for the reasons said above. Their mixture with the phosphines are crystalline, light yellow. These mixtures lose slowly carbon monoxide and melt at the same temperature as the original phosphine derivatives. The monocarbonylderivatives are orange yellow; they can be recrystallized and melt without decomposition. R E F b ~ t F.NCES [l] [2j [3] [4]
L, MATATa.~TA and M. ASOOL~TrA, • J . C . S . . , 1186 (1957). IDam/, , Acad. Naz. Lineei ,. [ V I l l i ~ , 43 (1955). L. MAI.ATRSTA and L. YALLARINO, q J. G, ~ . . , | ~ 7 (19~6). L. ]~|A.I~TliSTA • A. SACCo. • A n m d i .. 54. 134 (1954).
DISCUSSIONS
IWeimim, Hefts) - 1) l ~ m f e s s o r M a l a t e s t a , h a v e y o u i s o l a t e d t h i s c o m p o u n d or (PR,)sPt 2) W e have also done quite a lot of work tn this field and find that beqT~ene is, often firmly. attached to our products. Usually one or two molecules of benzene to each molecule of ph,tinum compound.
(PR~PtCsH.
Mahl/Utl - N o . b u t w e o b s e r v e d t h a t f r o m t h e b c q z e n e s o l u t i o n o f PtIP(C, Hs~Is a compound with a ratio P//P 1/2,5 separates. This compound contains some benzene.
Summary: New p l a t i n u m deri,~ttives, l m v i n g oxichttion n u m b e r zero, w i t l t t r i a r y l phospldnes, trtarylarsine~, t r h w y i p h o s p l d t e s are described. Some of these eompoumh are c o o r d i n a t i v e l y ~ttttrated, i. e. of the t y p e Ptu(PAra)t, o t h e r are u n s a t u r a t e d , of t h e t y p e
Ptot PAr s)a. The p h o s p h i n e d e r i v a t i v e s r e a c t s w i t h c a r b o n m o n o x i d e g i v i n g m i x e d cnrbonyl-phosphine derivatives.
The analogies between palladium and platinum compounds of the same oxidation number, i. e. 2 and 4, are considerable. Consequently, after the preparation, by one of us [1], of stable palladium(O) compounds, it appeared likely that similar • zerovalent ,~ compounds of platinum might be obtained. Therefore we began this investigation and its preliminary results were communicated in a short note [2]. The tirst palladium(O) compounds, bis(arylisonitryl)paUadium(O), were prepared from the dialogenodiisonitrylpalladium(ll) and excess of isonitryl with ethanolic potassium hydroxide. From these diisonitrylpalladium(O) compounds the tetrakis(triarylphosphine)palladium(O) and tetrakis(triarylphosphite)palladium(O) were obtained. The same phosphine and phosphite derivatives were prepared successively, by direct reduction of palladium(I/) compounds. The dihaiogenobis(aD.lisonitryl)platinum(//) are well known and form two series of compounds considered as structural isomers:
[l'/x2(CNl~,).,.l
and
[Pt(CXI-O,] [PIN,]
The compounds of the former series are very similar to the dihalogenolfis(arylisonitryl)palladium(IIL from which bis(arylisonitryl)palladium(O) had been prepared. All our attempts to obtain the presumed isonitDqderivatives of platinum(O) were, however, unsuccessful. Although many reducing agents "16
5~
LAMBERTO MALATESTA~ CONCETTA CARIELLO
cause changes in the solution of these dialogenides without any separation of metallic platinum, no product could be isolated. On the other hand the attempts to obtain the platinum(O) compounds with tervalent phosphorus donors, from platinum(I/) derivatives, gave the expected result. The best reducing agent for this purpose appears to be an ethanolic solution of anhydrous hydrazine, which reacts with the dialogenobis(triphenylphosphine)platinum(ll), or with the dihalogenobis(triphenylphosphite)platinum(II) and excess ligana as follows: PlI,(PR~)~ + 2,5 HtNNHt + 2 PR, =: Pl(PRs), + ~/s N, + 2 HsNNH3I forming the tetrakis(triphenylphosphine)platinum(O) and the tetrakis(triphenylphosphite)platinum(O), strictly analogous to the corresponding palladium(O) compounds. The triphenylphosphine derivative is yellow, crystalline, soluble in benzene and chloroform, almost insoluble in ethanol, and stable to air for many hours. The triphenylphosphite derivative, white and more soluble in ethanol, is quite similar. The cryoscopic determinations in benzene of both products show a dissociation which increases with time. The phosphine derivatives (as it is the analogous with palladium) can also be obtained both from dihalogenobis(triphenylphosphine)platinum(I/), triphenylphosphine and ethanolic potassium hydroxide or from chloroplatinate(I/) triphenylphosphine and ethanolic potassium hydroxide. The reduction could be due to phosphine: PIX,,(PRs), + 3 PR8 + KOH = PI(PR3), + POR8 + 2 K X + H~O or to the potassium ethoxide. This method cannot, of course, be used for the preparation of the phosphite derivative, in account of hydrolysis. The tetrakis(triphenylphosphite)platinum(O) can be obtained from the phosphine derivatives by ligand exchange: Pt(PR,), + 4 P(0R), = P t l P ( 0 R ) d , + 4 PRs
"Platinum appears to form these zerovalent compounds more readily than palladium, since, while the dihalogenobis(triphenylphosphine)palladium(I/) reacts with hydrazine (without excess of ligand) giving metal-
PT(O) COMPOI.YNDS WITH THIARYLPHOSPHINE
AND ANALOGOUS I.IGANDS
563
lic palladium, the dihalogenobis(triphenylphosphine)platinum(II) dispropotionates forming an unsaturated platinum(0) compound:
-i PtI,(PR~)2 + H.NNH, = 2 Pt(PRs), + Pt,ls (PRJ,(NH2NH,) + + 2N~ + 4 H I
The tris(triphenyl)platinum(0) is yellow, crystalline, stable to air. If this compound is monomeric, as it is probable, it must be a planar molecule, with s p* hybrid orbitals: while the PI (PR,), are almost certainly tetrahedral with s p* hybrid orbitals, as tetracarbonylnichel. Tris(triphenylphosphine)platinum(0), though coordinatively unsaturated, appears to be dissociated in benzene solution. This dissociation might be due to a replacement of the phosphine by a molecule of solvent Pt(PR3)~ + CsH.-----Pt (PRs)sC,Hs ÷ PRa.
A product, having the approximate composition of Pt [P(C,HJ,l,,snCsHs was in fact isolated. The product written as Pt, I,(N,H4)(PR3) s is supposed t o be ~-hydrazinebis(diiodotriphenylphosphine)platinum(lI), but it could not be yet isolated in a pure state and the analysis of the impure product gave only a qualitative evidence. Also the dihalogenobis(triphenylphosphite)platinum(ll)reactswith hydrazine giving the tricoordinated platinum(0)-phosphite derivative, i. e. pto[P(OR)s]s, which is white, crystalline, stable to air and dissociated in benzene solution, All the above reactions when carried out with tris-p.chlorophenylphosphine instead of triphenytphosphine, give only the tricoordinate Pt°-derivative Pl[P(CICstl,)s]s, even when a great excess of ligand is used. It is noteworth that, with palladium too, the corrispondent tricoordinated compound is formed. The reaction between tris(p.chlorophenylphosphine)platinum(0) and triphenylphosphite in excess gives a product vdth three molecules of phosphite and one molecule of phosphine:
Ptl(CIC, H,hP]s + 3 (CeHsO)sP = Pt(CIC,HJ~P[(C,H60)sP]s + + 2 P(CICsH4)s while with the other phosphines these mixed products can be obtained only using the calculated amount of phosphite:
pIoI ( C, H s)sP], + 3 ( Cl CsH, O)sP = PP( CsHs)sP[( Cl C J t ,O hP ],, This behavour suggests that platinum(O) tends to give three equivalent bonds, different from the fourth. The latter, which has perhaps
564
LAMBERTO MALATESTA, CONCETTA CARIELLO
less 7~ charachter than the others is not strictly necessary to the stability of the compound itselfand need not be formed as in the three coordinated derivatives described above. This behavior finds a parallel in the halogenotetraisonitrylrhodium(1) compounds [3], which have a isonitryl group less than required by coordinative saturation (four instead of five), and often bind a molecule of solvent. The phosphine and phosphite platinum(O) compound to not bind alchool but in contact with chloroform, they exchange a part of the ligand (about 0,5 tool) with the solvent. The Pt°-compounds with arylarsines are analogous to the saturated ones with phosphines. They could be obtained only by reduction with hydrazine and an excess of ligand on the dihalogeno-bis(triarylarsine) platinum(If):
PtCI,(R,As,) + 2 R,As + */,H , N N H , = Pt(RaAs), + ~/,N, + 2 HCI They are very similar to, but much less stable than, the phosphine compounds of the same serie. The Pl(O)-derivativeswere reacted with carbon monoxide under pressure in an attempt to prepare platinum(O) derivatives analogous to those of nickel, which had been obtained by action of phosphines and phospites on tetracarbonylnickel [4]. W e found that the phosphite compounds do not react with carbon monoxide while the phosphine compound add two molecules of it. As the coordination number of platinum(O) cannot exceed four, one must assume that the following reactions have taken place:
Pt(a,P), + 2 c o = Pt(Co),(Pa,), + 2 Pa, PI(R,P), + 2 C O = PI(CO),(PR,), + PR,
The phosphine displaced by the carbon monoxide cannot be removed from the reaction mixture because, if one tries to dissolve it in a solvent it reacts with the product substituting one carbon monoxide molecule:
PI(CO)t(R,P), + PR, = Pt(CO)(R,P), + CO Tris(p.chlorophenylphosphine)platinum(O) after treatment with carbon monoxide first and then with diethylether gives the coordinatively unsaturated compound Pt(CO)[P(CICeH4)s], wich may be formed either by the action of the solvent on a primary product which is coordinatively saturated:
PI(CO),[(CIC,H.),P], = Pt(CO) [(CIC,H.)aP], + CO
PT(O) COMPOUNDS 'WITH TRIARYLPHOSPHINE AND ANALOGOUS LIGANDS
565
or by reaction of a coordinatively unsaturated primary product with the displaced phosphine: I't(CO),(ClC, II,)aP + (CICeH,)aP = Pl(CO)[(CICsH,)aP]., + CO These bicarbonylderivatives were not isolated for the reasons said above. Their mixture with the phosphines are crystalline, light yellow. These mixtures lose slowly carbon monoxide and melt at the same temperature as the original phosphine derivatives. The monocarbonylderivatives are orange yellow; they can be recrystallized and melt without decomposition. R E F b ~ t F.NCES [l] [2j [3] [4]
L, MATATa.~TA and M. ASOOL~TrA, • J . C . S . . , 1186 (1957). IDam/, , Acad. Naz. Lineei ,. [ V I l l i ~ , 43 (1955). L. MAI.ATRSTA and L. YALLARINO, q J. G, ~ . . , | ~ 7 (19~6). L. ]~|A.I~TliSTA • A. SACCo. • A n m d i .. 54. 134 (1954).
DISCUSSIONS
IWeimim, Hefts) - 1) l ~ m f e s s o r M a l a t e s t a , h a v e y o u i s o l a t e d t h i s c o m p o u n d or (PR,)sPt 2) W e have also done quite a lot of work tn this field and find that beqT~ene is, often firmly. attached to our products. Usually one or two molecules of benzene to each molecule of ph,tinum compound.
(PR~PtCsH.
Mahl/Utl - N o . b u t w e o b s e r v e d t h a t f r o m t h e b c q z e n e s o l u t i o n o f PtIP(C, Hs~Is a compound with a ratio P//P 1/2,5 separates. This compound contains some benzene.