Indian Jonrnal of Chemistry Vol. 20A, July 1981, pp. 673-676 Rhodium Nitrosyl Complexes K. K. PANDEY & U. C. AGARWALA* Department of Chemistry. Indian Institute of Technology. Kanpur 208016 Received 27 October 1980; revised and accepted 12 January 1981 " The reactions of nitrosyl chloride and nitrosyl bromide with rhodinrn(I) complexes containing triphenylphos- phine and triphenylarsine have boon studied. These reactions result in the formation of the complexes of the type [Rh(eO)(NO)eIXL.] (X = CI, Br; L = PPh 3 , AsPh a ) and Rh(NO)X 3 L 2 • Reactions of Rh(CO) (NO)eIX(PPh 3 ). (X = Cl, Br) with hydrazine hydrate afford RhH(eO)(PPh s ). and a highly hygroscopic red complex [Rh(N 2 H.)2]X (X = Cl or Br). The probable structures of these complexes have boon proposed on the basis of elemental analyses, spectroscopic (IR, UV and EPR) and magnetic data. N ITROSYL halides have been utilized to intro- duce nitrosyl functionality in transition metal complexes'r!". The reactions of NOX (X = CI or Br) with the coordinatively unsaturated complexes may be additive or with coordinatively saturated compounds substitutive, each I OX added may displace ligands capable of donating to the total of four electrons to the metal. In this paper, the reactions of nitrosyl chloride and nitrosyl bro- mide with Rh(CO)CI(PPha)z, Rh(CO)Cl(AsPbah and RhH(CO) (PPh 3 )a have been described. The structures of the resulting products have been proposed on the basis of results obtained by the chemical ana- lyses, spectroscopic analyses (IR and EPR), mag- netic measurements and various chemical reactions. Materials and Methods All the chemicals used were either chemically pure or of AR grade. The solvents were dried by standard procedures and deaerated just prior to use; all manipulations were performed in an at- mosphere of purified nitrogen. (Carbonyl) (chloro) bisttriphenylphosphine) rho- dium(I), (carbonyl) (chlorojbis (triphenylarsinejrho- diumrl], (carbonyl)(hydrido)tris(triphenylphosphine) rhodium(I), nitrosyl chloride and nitrosyl bromide were prepared by the literature methods-v+'. Reaction of NOCI with [Rh(CO)C1LuJ (L=PPh 3 or AsPh 3 ) - Nitrosyl chloride gas was passed through a stirred solution of [Rh(CO)ClLzJ (0.2g) in dichloro- methane (15 ml) for I hr. A vigorous reaction occurred and -the colour of the reaction mixture changed to red. It was concentrated under re- duced pressure and the residue extracted with dichloromethane (2ml). A sparingly soluble yellow crystalline compound, Rh(CO)(NO)ClzL u sepa- rated out which was filtered, washed with ethanol and ether and dried in vacuo, The filtrate was dried at reduced pressure and the resulting crude product analysed for Rh(NO)CI 3 L z . Reaction of NOBr with [Rh(CO) C1L 2 ] (L=PPh a or AsPh 3 ) - A solution of nitrosyl bromide (2ml) was added to a solution of Rh(CO)CILz (0.2g) in dichloromethane (lOml). It was kept for 2 hr and the complexes Rh(CO)(NO)ClBrL 2 (L=PPh 3 , AsPh 3 ) (orange), Rh(NO)Br 3 (PPh:J2. (red brown) and RhBr 3 (AsPh a )2 (red brown) were isolated by a procedure given above. Reaction of NOX (X=CI, Br) with RhH(CO) (P Ph 3 h- The reaction of RhH(CO)(PPb 3 )3 (O.2g) with NOX (X=Cl or Br), gave complexes Rh(CO) (NO)X z (PPh 3 h (X=Cl, Br) and Rh(NO)X 3 (PPh 3 )2 by procedures similar to those given above. Reaction of hydrazine hydrate with Rh(CO)(NO) CIX(PPh 3 )'}. (X=CI or Br) - The complex Rh(CO) (NO)CIX(PPh 3 )2 (0.08g) was placed in a flask and a solution of hydrazine hydrate (O.Sml) in methanol (Sml) and CHeCl'}. (2ml) added to it. The solution was stirred for 30 min whereby a yellow compound, RhH(CO) (PPh 3 )3 separated out which was filtered and washed with water, ethanol and n-hexane and dried in vacuo. When the reaction mixture was stirred for 3 hr instead for 30 min, the colour of the reaction mix- ture changed to reddish brown with the precipita- tion of the yellow RhH(CO)(PPh 3 )2 which was filtered off. n-Hexane was then added to the red filtrate when pure red complex, [Rh(N u H 4 )2JCI pre- cipitated out. It was filtered and washed several times with n-hexane. The colourless filtrate, after the removal of [Rh(N z H 4 )2]CI was evaporated to dryness and from the residue OPPh 3 was separated which was characterized by chemical analyses, IR and m.m.p. Reaction of hydrazine hydrate with Rh(NO)Xa (PPh 3 )2 (X=CI, Br) - Hydrazine hydrate (O.Sml) in methanol (Sml) was added to a stirred solution of Rh(NO)X 3 (PPh 3 )2 (O.08g) in dichloromethanc (5 ml). The red complexes, [Rh(N z H 4 )2]X were isolated by the similar procedure as given in the preceding preparation. Analyses - Halogen estimation was carried out by standard methods". For the estimation of phosphorus and arsenic, samples were decomposed with sodium peroxide, sugar and sodium nitrate in the ratio 20: I :3 in a Parr bomb crucible and 673
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Indian Jonrnal of ChemistryVol. 20A, July 1981, pp. 673-676
Rhodium Nitrosyl ComplexesK. K. PANDEY & U. C. AGARWALA*
Department of Chemistry. Indian Institute of Technology. Kanpur 208016
Received 27 October 1980; revised and accepted 12 January 1981
"The reactions of nitrosyl chloride and nitrosyl bromide with rhodinrn(I) complexes containing triphenylphos-phine and triphenylarsine have boon studied. These reactions result in the formation of the complexes of the type[Rh(eO)(NO)eIXL.] (X = CI, Br; L = PPh3, AsPha) and Rh(NO)X3L2• Reactions of Rh(CO) (NO)eIX(PPh3).
(X = Cl, Br) with hydrazine hydrate afford RhH(eO)(PPhs). and a highly hygroscopic red complex [Rh(N2H.)2]X(X = Cl or Br). The probable structures of these complexes have boon proposed on the basis of elemental analyses,spectroscopic (IR, UV and EPR) and magnetic data.
NITROSYL halides have been utilized to intro-duce nitrosyl functionality in transition metalcomplexes'r!". The reactions of NOX
(X = CI or Br) with the coordinatively unsaturatedcomplexes may be additive or with coordinativelysaturated compounds substitutive, each I OX addedmay displace ligands capable of donating to thetotal of four electrons to the metal. In this paper,the reactions of nitrosyl chloride and nitrosyl bro-mide with Rh(CO)CI(PPha)z, Rh(CO)Cl(AsPbah andRhH(CO) (PPh3)a have been described. The structuresof the resulting products have been proposed onthe basis of results obtained by the chemical ana-lyses, spectroscopic analyses (IR and EPR), mag-netic measurements and various chemical reactions.
Materials and MethodsAll the chemicals used were either chemically
pure or of AR grade. The solvents were dried bystandard procedures and deaerated just prior touse; all manipulations were performed in an at-mosphere of purified nitrogen.
(Carbonyl) (chloro) bisttriphenylphosphine) rho-dium(I), (carbonyl) (chlorojbis (triphenylarsinejrho-diumrl], (carbonyl)(hydrido)tris(triphenylphosphine)rhodium(I), nitrosyl chloride and nitrosyl bromidewere prepared by the literature methods-v+'.
Reaction of NOCI with [Rh(CO)C1LuJ (L=PPh3 orAsPh3) - Nitrosyl chloride gas was passed through astirred solution of [Rh(CO)ClLzJ (0.2g) in dichloro-methane (15 ml) for I hr. A vigorous reactionoccurred and -the colour of the reaction mixturechanged to red. It was concentrated under re-duced pressure and the residue extracted withdichloromethane (2ml). A sparingly soluble yellowcrystalline compound, Rh(CO)(NO)ClzLu sepa-rated out which was filtered, washed with ethanoland ether and dried in vacuo,
The filtrate was dried at reduced pressure andthe resulting crude product analysed for Rh(NO)CI3Lz.
Reaction of NOBr with [Rh(CO) C1L2] (L=PPhaor AsPh3) - A solution of nitrosyl bromide (2ml)was added to a solution of Rh(CO)CILz (0.2g) in
dichloromethane (lOml). It was kept for 2 hrand the complexes Rh(CO)(NO)ClBrL2 (L=PPh3,
AsPh3) (orange), Rh(NO)Br3(PPh:J2. (red brown)and RhBr3(AsPha)2 (red brown) were isolated by aprocedure given above.
Reaction of NOX (X=CI, Br) with RhH(CO)(P Ph3h - The reaction of RhH(CO)(PPb3)3 (O.2g)with NOX (X=Cl or Br), gave complexes Rh(CO)(NO)Xz(PPh3h (X=Cl, Br) and Rh(NO)X3(PPh3)2
by procedures similar to those given above.Reaction of hydrazine hydrate with Rh(CO)(NO)
CIX(PPh3)'}. (X=CI or Br) - The complex Rh(CO)(NO)CIX(PPh3)2 (0.08g) was placed in a flask and asolution of hydrazine hydrate (O.Sml) in methanol(Sml) and CHeCl'}. (2ml) added to it. The solutionwas stirred for 30 min whereby a yellow compound,RhH(CO) (PPh3)3 separated out which was filteredand washed with water, ethanol and n-hexane anddried in vacuo.
When the reaction mixture was stirred for 3 hrinstead for 30 min, the colour of the reaction mix-ture changed to reddish brown with the precipita-tion of the yellow RhH(CO)(PPh3)2 which wasfiltered off. n-Hexane was then added to the redfiltrate when pure red complex, [Rh(NuH4)2JCI pre-cipitated out. It was filtered and washed severaltimes with n-hexane. The colourless filtrate, afterthe removal of [Rh(NzH4)2]CI was evaporated todryness and from the residue OPPh3 was separatedwhich was characterized by chemical analyses,IR and m.m.p.
Reaction of hydrazine hydrate with Rh(NO)Xa(PPh3)2 (X=CI, Br) - Hydrazine hydrate (O.Sml)in methanol (Sml) was added to a stirred solutionof Rh(NO)X3(PPh3)2 (O.08g) in dichloromethanc(5 ml). The red complexes, [Rh(NzH4)2]X wereisolated by the similar procedure as given in thepreceding preparation.
Analyses - Halogen estimation was carried outby standard methods". For the estimation ofphosphorus and arsenic, samples were decomposedwith sodium peroxide, sugar and sodium nitratein the ratio 20: I :3 in a Parr bomb crucible and
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extracted with water. The solution was neutralizedwith H2S04 and excess of cone. H2S04 (0.5 ml)added. It was heated till the evolution of SOafumes ceased, cooled and diluted with water. Fromthe filtrate of the solution phosphorus was estimatedas phospho-ammonium molybdate. For the estima-tion of arsenic, the above solution was diluted to100 ml. To an aliquot (25 ml) of this solution wasadded water (40 mI), sodium bicarbonate (Sg) andstarch solution (2 mI). The solution was swirleduntil the sodium hydrogen carbonate had dissolved.It was titrated slowly with standard iodine solution,to the first blue colour. In order to estimate rho-dium-", samples were decomposed with cone. H2S04
and cone. HN03. The solution was evaporated todryness and extracted with water. Rhodium wasestimated in the water extract as [Co(NH3)6J3+[(Rh(N02)6P-'
Physical measurements - Infrared sepctra of thecompounds were recorded in KBr on a PerkinElmer model-S80 in the 4000-250 cm " range. Con-ductivity measurements of the compounds weremade on an Elico conductivity meter type CM-SOfor millimolar solutions in nitrobenzene. The elec-tronic spectra were recorded in chloroform solu-tions on a Cary Model-I7.
Results and DiscussionThe analytical data of the complexes are given
in Table 1. Reactions of NOCI with [Rh(CO)C1L2] (L=PPha or AsPh3) furnish yellowish crystal-line complexes Rh(CO)(NO)CI2L2 and red browncomplexes Rh(NO)CI3L2' NOX (X=CI or Br)reacts with RhH(CO) (PPha)a to give Rh(CO)(NO)X2
(PPhah and Rh(NO)X3(PPhah. NOBr reacts with[Rh(CO)CIL2J (L=PPha or AsPha) to give Rh(CO)-(NO)ClBrLa and RhBra(AsPh3)2 respectively. Treat-ment of Rh(NO)X3(PPhah (X=CI or Br) withdichloromethane-petroleurn ether affords diamag-netic complexes Rh(NO)X2 (PPhahCH2CI2 pro-bably by reduction followed by the loss of a chlorideion".
These complexes reveal two interesting featuresin their IR spectra+ (a) All the complexes Rh(NO)Xa(PPhS)2' Rh(NO)CI3(AsPh3)z and Rh(NO)Xz(PPhahshow an intense iband around 1400 besides the bandsdue to PPh3 or tsPha. (b) The complexes [Rh(NO)-ClaLz] (L=PPha or AsPha), Rh(NO)Br3(PPha)2 areparamagnetic.
The compound having the composition Rh(NO)CI2-(PPh3h was reported earlier8,17,18. These authorsindicated the occurrence of a band in its IR spec-trum at 1630 and assigned it to v(NO). But thecompounds, Rh(NO)X2(PPhah reported here(compds 9 and 10 in Table 1) do not show anyband in this region. It is, therefore, felt that thepresent compounds may be different from thatreported in literature. These complexes are non-electrolytes and diamagnetic, suggesting the com-plexes to be non-ionic and rhodium in either+1 or +3 oxidation state. If 1390 band in 9and 10 is assigned to '1(NO), the oxidation state ofrhodium in the complexes can not be + 1, since inthat case NO should be bonded as NO+, a specieswhich absorbs around 1800 em= in the IR. Further,for NO bonded as NO-, the position of v(NO)(1390) seems to be relatively low. However, recentlyDolcetti et af.19 have reported an iridium complex,
[Ir(NO) (CHaCNMPPha)2] [PF6]2 in which theyhave assigned a band at 1560 to coordinated NO-.However, X-ray data indicate Ir-N-O angle to be1100 which is less as compared to ones reported incomplexes having NO-. The reason which theyhave assigned for this peculiar behaviour of NO inthe six-coordinate complex is that in the five-co-ordinated one there is an accumulation of extraelectron density at the iridium by the sixth ligand.It could be possible that NO group in our six-coordinate Rh(III) complexes may also be showingsimilar behaviour. This could only be checked byan X-ray analysis.
There could, however, be another possibility forthe low values of v(NO). Cenini and coworkers='reported a few nitrosyl derivatives of rhenium show-ing band due to v(NO) around 1375. They pre-sumed that the NO in these complexes was bondedas HNO in which case v(NO) should come around1400. There could thus be a possibility of the pre-sence of bonded HNO in our complexes too. Butin case the presence of bonded HNO is presumedin the complexes, bands due to v(NH) and S(NH)around 3100 and 1600 respectively should also beexpected. The absence of such bands in the IRspectra, however, suggested that they do not haveHNO bonded as ligand in them.
The possibility of the presence of NO as N202
is also ruled out because of the absence of character-istic bands of N20i.
It is, therefore, presumed that these compoundscontain NO as NO- with Rh-N-O bond anglepossibly below 1200
• But this assignment is onlytentative and the definite conclusions should not bedrawn solely on the IR data.
Another interesting feature of this study is theformation of two paramagnetic complexes havingthe general composition Rh(NO)X3(PPh3h (compds6, 7, Table 1). The paramagnetism corresponds toone unpaired electron (-1.9 B.M.). Accordinglyrhodium in these complexes may be either in +2 or+4 oxidation state. Another possibility might bethat NO radical be trapped in the crystal latticewhich might impart paramagnetism to the com-plexes, but it is highly improbable that one mol ofNO radical might have been trapped in one mol ofrhodium complex to give the paramagnetism cor-responding to one unpaired electron in the com-plexes. Another possibility of paramagnetism isthe presence of Rh(II) or Rh(IV) compounds asimpurities. But the analytical results of the com-plexes prepared under various experimental condi-tions are highly consistent, which made us to believethat paramagnetism is not due to any other impuri-ties. Since there is already a nitrosyl of Rh(II)known-' which has paramagnetism correspondingto one unpaired electron, there is a probability ofthese complexes of Rh(IV). Further the EPRspectra of these complexes (Fig. 1) shows a broadband corresponding to the g value of 2.3. Thebroadness of the band indicates that the paramag-netism of the complexes is not due to the presenceof free radical which generally gives sharp bandsin the EPR spectra. It is hard to decide whether
these complexes are of Rh(II) or Rh(IV). Sinceband due to v(NO) appears at 1395 in their IRspectra, NO is linked possibly as NO- in the com-plex.
The electronic spectra of Rh(NO)X3(PPh3)2 exhibita moderately intense band at 490 nrn (E=800) anda number of intense bands at 400, 375, 355 and300 nm. In the visible spectrum of spin-paired d5_
system, bands due to electron transfer from filledmolecular orbitals mainly on the ligand to the holeavailable in the t2f1 orbitals are prominentw, Thesebands are therefore assigned to the charge transferbands. Rhodium in +4 oxidation state showsgenerally charge transfer bands because of its highoxidizing state.
These arguments therefore suggest that the com-plexes should contain rhodium in +4 oxidationstate. These conclusions should however be takenonly as tentative and more experimental work isneeded before a definite oxidation state of rhodiumin these complexes is arrived at.
The JR spectra of Rh(CO) (NO)CIX(PPh3/AsPh3)z(X=CI, Br) and Rh(CO)(NO)Br2(PPh3/AsPh3h(Cornpds 1 to 5; Table 1) exhibit strong bandsin the region 2095±5 a range for v(CO) character-istic of rhodium(III) carbonyl complexes and at1630, due to v(NO). The corrected v'(NO) byIbers empirical rules+" is calculated to be 1600 cm='which could be assigned to the bent nitrosyl. Theshifting of the position of v(CO) towards higherwave number may possibly be due to the strong,primarily a-bonding trans-effect of the presumedtrans NO- group. The complexes are diamagnetic.These facts support that the oxidation state ofrhodium in these complexes is +3.
The far IR spectra of the complexes Rh(CO)(NO)CIXL2 (compds 1-5, Table 1) show bands due to
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v(Rh-Cl) at 340 (Cl trans to Cl or Br) andv(Rh-Br) at 275. Thus the probable structures ofRh(CO)(NO)CIXL2 may be represented by struc-ture (I)
0./
NL"I
X X Cl or Br/
Rh/ I -,
CI L L PPh;; or AsPb3
COI
Reactions of Rh(CO)(NO)X2(PPh3h (X=CI, Br)with hydrazine hydrate give Rh(H)(CO)(PPh3)3and hygroscopic complex [Rh(NzH4)2]X (compds12, 13). The complexes [Rh(NaH4)2]X are also ob-tained by the reaction of Rh(NO)XiPPh3)2 andhydrazine hydrate. The conductivity of [Rh(N2H4)2]X(X=CI or Br) are in the range 98.6 and 96.7 ohm ?
em-mol'? which suggests the complexes to be 1:1electrolyte. The conductivities of other rhodium(1II)complexes are found to be very low (AM = 2 to10 ohrn= em> mol ") which rules out the ionicnature of these complexes. The 1R spectra of[Rb(N2H4)z]X exhibit bands at 1320, 1100, 950,800 and 620. These are the characteristic bandsdue to the coordinated hydrazine. The v(N-N) at950 indicates the presence of bridging hydrazinemoiety>'.
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