4212
Journal of the American Chemical Society
/
101:15
/ J u l y 18, 1979
Hydration and Reduction of Carbon Dioxide by Rhodium Hydride Compounds. Preparation and Reactions of Rhodium Bicarbonate and Formate Complexes, and the Molecular Structure of RhH2(02COH)(P(i-Pr)3)2 T. Yoshida,'" David L. Thorn,lb T. Okano,'" James A. Ibers,*lb and S. Otsuka*la Contribution f r o m the Department of Chemistry, Faculty of Engineering Science, Osaka Unicersity, Toyonaka, Osaka, 560 Japan, and the Department of Chemistry, Northwestern Unicersity, Ecanston, Illinois 60201. Rrceiwd Januarj) I I , I979
Abstract: Reaction of Rh( I)--hydridecomplexes RhH(P(;-Pr)3)+ RhH(Nz)(PPh(t-Bu)2)z,and RhrHz(p-N2)(P(c-C6H I 1 ) 3 ) ~ with COz i n the presence of H 2 0 has been found to afford novel dihydrido bicarbonato complexes RhH2(02COH)Lz (1, L = P(i-Pr)3; 2. L = PPh(t-Bu)>; 3, L = P(c-C6H, 1)l).The crystal and molecular structure of 1.has been determined a t - 160 OC. The complex RhH2(OzCOH)(P(i-Pr),)> (1) crystallizes in the monoclinic space group Cih-P?I / c . with four formula units i n a cell of dimensions n = 15.82 ( I ) A, b = 10.88 ( I ) A, c = 15.49 ( I ) A. 6 = 1 14.5 ( I ) O . c' = 2428 A3,In the solid state 1 con-
sists of distorted octahedral Rh( I I I ) centers coupled by intermolecular hydrogen bonding between bicarbonato ligands. These dihydrido bicarbonato complexes, and analogous dihydrido formato complexes, reduce C O ? to form Rh( I ) carbonyl bicarbonato and formato complexes and HzO.
Introduction Although formato complexes were never observed i n the The use of transition-metal compounds for the fixation direct reaction of these Rh( I ) hydride complexes with CO1, of COz is of considerable interest in view of the promising even in the absence of water, formato complexes were easily utility of COz as a carbon resource.2,3Reactions of COz with obtained when the Rh(1)-hydride complexes were treated with transition-metal complexes have sometimes resulted in the formic acid. These formato complexes are exact analogues of formation of COl while reactions with metal the bicarbonato complexes and show very similar reactivicomplexes containing M-H,z-4.Y-I 1 M-C 2 - 4 . 7 . 1 2 . 1 3 Mties. 0,3.4.'4.' or M-N2-4.16,'7bonds often afford the corresponding Experimental Section insertion products. Generally these reactions are carried out under anhydrous conditions; thus little is known about the All reactions and manipulations were carried out under an atmoreactions of COz with transition-metal compounds in aqueous sphere of dinitrogen or carbon dioxide. ' H N MR spectra were remedia. corded on J E O L JNM-4H-100 or JNM-C-60 H L spectronietcrs.31P spectra on a Varian CFT-20 spectrometer a t 32.199 V H 7 . nnd IK Motivated by efficient catalytic activity of Rh( 1)hydride spectra on a Hitachi Model 295 spcctromctcr. All rcportcd IK complexes, e g , RhH(P(i-Pr),)3 and RhzHz(p-Nz)(P(cI'rcquencies are from Kujol mull spectra. Literature methods lvcrc C6Hl 1)3)4,18 for the water-gas shift reaction,Iy we have carried uscd for the preparation of' rrcr/r.s-RhH(~\'2)(PPh(r-Bu).)z,?~ out detailed studies of the reaction of these Rh(1) hydrides with R h . H z ( p - N z ) ( P ( c - C h H I I ) ~ ) j , ' x RhH(P(i-Pr)3)3,IX and transC O ? in aqueous organic media. Hitherto unknown dihydrido K h ( O H ) ( C O ) L ? ( L = PPh3. P(i-Pr)3).2hThe compound R h ( 0 H ) bicarbonato compounds RhHl(O?COH)L? (1, L = P(i-Pr)]; by a method similar to that em( C O ) ( P ( C - C ~ H I ~was ) ~ )prepared ? 2 , L = PPh(t-Bu)?; 3, L = P ( C - C ~ H ~were ~ ) ~ obtained. ) ployed for Rh(OH)(CO)(PPh,)?. Carbon dioxide \+:is obtained from During the course of our studies we found a surprisingly facile f-uji Midori, Ltd. and was used without purification. Infrared spectral reduction of CO? by these dihydrido Rh(ll1) compounds. This data for the bicarbonato complexes iind N M R spcctral data are reduction, a reversal of the water-gas shift reaction, has recontained in Tables I and I I . Satisfixtory clenicnt;iI analyses for C. I 1 hxve been obtained for all compound\ described hcrcin cxccpt 7 and ceived very little attention,'" and here we have examined it in 1 0 (vide infra). detail. Bis(triisopropylphosphine)dihydridobicarbonatorhodium(llll, Since the usual product of the reaction of C 0 2 with a tranRhH2(02C'OHXP(i-Pr)3)2(11. Method A. Carbon dioxide. not predried, sition metal hydride complex is a formate complex,' 4.y I \+;is bubbled into a yellow solution of RhH(P(i-Pr),)j ( I 3 0 nig, 0.2 these dihydrido bicarbonato complexes were originally believed mniol) in dry n-hexane (10 niL) at room temperature for I h . Thc to be carbon dioxide-formato complexes. It was in the hope resulting colorless solution was stirred for a n additional 20 h. The of confirming the presence of a weakly bound COl molecule solution was then evaporated and dried in vacuo and the solid residue that the present X-ray structure determination of 1 was un\ \ a s recrystallized from toluene-n-hexane to give colorless crystals dertaken, and the true nature of the complexes was revealed. or 1 (55 nig, 48(10), mp 100 OC dec. Method B. The compound 1 w;is also prepared by stirring a solution These dihydrido bicarbonato complexes 1-3 are the first oI'KhH(P(i-Pr)3)3 (585 mg. I minol) in 10 mL of wet T H F (10'70 $-bicarbonat0 compounds reported from the reaction of CO,, water by volume) under I a t m of CO? for Z h. After the reaction H 2 0 , and low-valent transition-metal complexes. A similar mixture w a s dried in v;icuo. 1 w a s obtained from the residue by rereaction of PdMez(PMe3)2 with CO? and H 2 0 affords the in ca. 85% yield. TI-bicarbonato compound trans-PdMe(O2COH)(PMe3)?.?l crystallii.ation Bis(di-~ert-butylphenylphosphine)dihydridobicarbon~torhodium(lll), Participation of H l O has been suggested in the formation of RhH2(02COH)(PPh(t-B~12)2 (2). A toluene solution of RhH(N2)Rh?(O?CO)(PPh3)5 from the reaction of RhH(PPh,),, ( n = ( P P h ( t - B u ) ? ) ?was treated with CO2 as in method A above. Recrys3, 4) with C O Z . ?Other ~ carbonato complexes have been ret;illi7ation of the dried residue from toluene-n-hexane gave colorless ported from the reaction of C 0 2 with Pt(PPh3)3 in the presence crbstals of 2. mp 120 'C dcc. yield 17% of 0 2 , 1 3 and from the disproportionation of CO? into C03*Bis(tricyclohexylphosphine)dihydridobicarbon~torhodium(lll~, R ~ ~ ( ~ ( O ~ C O H X P ( C - CO1( C ~ HI2 ~~ mL. I ~0.5 I~ nimol) ~ ~ )w. and CO in a Mo-CO2 complex.'4 0002-1863/79/I501-4212$01 .OO/O
0 I979 American Chemical Society
Ibers, Otsuka, et al. / Rhodium Bicarbonate and Formate Complexes
4213
Table I. Infrared Dataa of Bicarbonato Complexes VRh-H
or
UC-0
VOH
2120 m, 2140 m 21 45 m, 2220 m 2138 m, 2158 m c (21 10, 2160) I942 s I942 s 1900 s 1952 s I968 s
or voo
vcio
60HO
2650m 2660m 2640m
1587 s 1583s 1585s
b b 1410 w
2650 w 2087 w 2657 w 2600 w 2650 w 2620 w 2055 w
I608 s I590 s I575 s
1420 s 1062 s I402 w 1413 s I430 s d I405 s
1615 s
I600 s I618 s 1615 s
1050 s
VC-0
+ VC=O + 6 0 H O
TCO,
I338 s 1340s 1340 s
792 m 802 m 790 m
1355 s 1405 s 1345 s 1350 s 1350 s I367 s I392 s
821 m 821 m 822 m 823 in 819 m 830 m 830 in
Sample recrystallized from I ) , stretching: 6,in-plane bending: H , out-of-plane bending. The band probablyoverlaps with that of Nujol. toluene. T h e value in parentheses is for the sample recrystallized from T H F . T h e band is a composite of 6 0 ~ 0and vp.ph. CI Y H ~ s O ~ P Z R ~ 486.42 amu s - 1 6 0 "C 15.82 ( I ) A 10.88 ( I ) A
15.49 ( I ) A 114.5 ( I ) ' 2428 A3 4 I .33 g cm-3 I .28 g (25 'C) C';h - P2'/C 0.2 I X 0.44 X 0.39 mm prismatic pl_te, fazes of forms 1 IOO}, 1 102). I I 1 1 1 0.0472 mm3 Mo Kcu (X(Mo Kcul) = 0.709 30 A) from monochromator 8.35 cni-'
lineiir absorption cocfficient of T H F as an internal reference was stirred under I a t m of CO, for 0.738-0.85 I transmission factors 20 h at room temperature. VPC analysis (Porapak Q, 2.5 ni, 140 "C) 2.8' takeoff angle of the reaction solution showed the quantitative formation of water. in speed 2' in 2H/min H? was not detected in the vapor phase. The I R spectrum of the conscan range 0.9' below K a l peak to 0.9' above K a z centrated reaction mixture showed the carbonyl formato complex 9 peak ( I 954 vs, I633 s, 13 I O s) as the major product together with a small background counts I O s with rescan option amount of Rhl(CO)r(OzCO)(P(i-Pr)3)4 (8) (1934, 1533 em-'). 2H limits 4.0-59.2' Upon recrystallization of the dried residue from ether analytically pure 238 final no. of variables (9) was obtained as pale yellow crystals Rh(CO)(O>CH)(P(i-Pr)3)2 unique data used, Fo2 5844 (180 mg, 52%), mp 106 'C dec. > 3u(Fo2) Method B. RhH(P(i-Pr)3)3 (162 mg. 0.28 mmol) and formic acid 0.028 K (27 nig, 0.6 mmol) were added to acetone ( I O mL) and the mixture 0.035 KM was stirred for 15 inin at room temperature. Treating the concentrated crror in observation of I .41 electrons reaction mixture as in A above gave 9 (71 nig, 51%). unit weight Bis(tricyclohexylphosphine)carbonylformatorhodium(l~,Rh(C0)( O ~ C H ) ( P ( C - C ~ (10). H ~ ~This ) ~ ) compound ~ was obtained iis pale yellow crystals in 60% yield from the reaction of RhH2(02CH)(P(cfor diffraction studies were carefully handled in inert atmospheres ( A r or N l ) . ChHj 1)3)2 (5, 210 nig, 0.33 mmol) with C 0 2 as in method A for 9, mp 160- I67 OC dec. The compound 10 was also obtained in poor yield T h e data set was collected on a computer-controlled Picker diffrom the direct reaction of R ~ ? H ~ ( ~ - N ~ ) ( P (1)3)4 ~ - Cwith ~ Ha Ilarge fractometer with the crystal at E - I60 'C in a stream of cold nitroexcess of formic acid, the major product being the dihydrido formato g ~ n . Cell ' ~ constants obtained from I8 hand-centered reflections28 complex 5. IR of 1 0 1945, 1630, I292 cm-I. Anal. (C38H6703P~Rh) a t t h i s t e m p e r a t u r e a r e a = 1 5 . 8 2 ( I ) A , b = 1 0 . 8 8 ( I ) A . c = 15.49 C , H; C: calcd, 61.95; found, 62.98. ( I ) A, p = 114.5 (I)'. V = 2428 A3 (X(Mo KO!') = 0.709 30 A). A Reaction of l3C02 with R ~ H ~ ( O ~ C O H Y P ( C(3). -C A~ pyridine H~~~~) ~ of 7462 reflections in the range 4.0 5 28( MoKcu) I59.2' was total solution of 3 (20 mg. 0.03 nimol) was stirred with I3CC), (23 mL at collected. From these the 5844 unique reflections having F,? > 1 atm, 1 .O mmol; generated from the reaction of BaI3C03 (90% "C) 3u(F,') were used in the refinement. A set of seven standards, with aqueous HCI) for 0.7 h a t room temperature. The IR spectrum rcmcasured every 100 reflections during the data collection, showed of the concentrated residue showed the near-quantitative formation no significant intensity fluctuations. Further information regarding of Rh(CO)(OpZOH)(P(c-ChH 1 1 ) 3 ) ? ( 6 ) .with incorporation of "C the data collection is given in Table I l l . into both the carbonql and bicarbonato ligands. The ratio [ ' * C O ] / Solution and Refinement of the Structure. For all nonhydrogen ; i t o m the usual scattering factors were used:?9 anomalous dispersion [ "CO] assessed from the IR band intensities of the terminal carbonyl termsr9 were included in F , for rhodium and phosphorusatoms. The 0 VI3CO 1900 cm-I) was 0.17, with a stretching modes ( ~ 1 2 ~1942, similar "C/"C ratio found from the bicarbonato stretching hydrogen scattering factors of Stewart. Davidson. and Simpson were used for all hydrogen atoms.3o The function minimized during re~ U I ~ C O 1575 , em-[). Assuming full scramfrequencies ( V I Z C O1608, bling of the bicarbonato ligand of 3 with I3CO2 prior to reduction, the I'incment was zw((F,,l - IF,()? calculated ratio is 0.14. The rhodium and phosphoruz, a t o m were easily found from a Reaction of I2CO2 with Rh(13COH0213COHXP(c-C~H~~i~)~ ( 6 ) .The f'attcrson map,31and all remaining nonhydrogcn atoms were located 13C-labcledcomplex 6 prepared above was dissolved in pyridine (5 by Fourier methods. After several cycles of isotropic refinement and mL) and stirred under 1 atni of l T O ?for 0.7 h a t room temperature. one cycle of anisotropic rcfinenient. the positions of most of the isoThe IR spectrum of the concentrated residue showed essentially propyl hydrogen atoms. the hydroxy hydrogen atom. and the two complete convcrsion of the I3C-bicarbonato ligand into "C-bicarhydrido ligands were clcnr on a diffcrcnce Fouricr map. The isopropyl bonate. T h c [ 1 2 C O ] / [ ' 3 C O ]ratio of the carbonyl ligand remained hydrogen atoms were placed in idealixd locations ( C - H = 0.95 A, unchanged. tetrahedral angles), cach given an isotropic thermal parameter B 1 .O X-ray Data Collection. Diffraction studieh wcrc performed on single A' grcater than the equivalent B of the carbon atom to which it is crystals of I , RhH2(02COH)(P(;-Pr)3)2, prepared as above and reattached, and held fixed during all subsequent refinement. Two further crystalli7cd from toluene-hexane. Preliminary room-temperature cycles of anisotropic refinement, in which both hydrido and the hyX-ray photographic data showed the crystals to be monoclinic, with droxy hydrogen atoms were refined isotropically. resulted in conversy\tematic absences (h01, I odd; O k O . h odd) which are consistent with gence with K = 0.028. R,. = 0.035. A final difference Fouricr synthesis revealed no peaks above 0.5 e / A 3 but there were holes of ca. the spacc group C':I,-P21/ c . The initial u n i t cell parameters from the photographic datti led to a dcrisitq of I .30 g/cm3 calculated for four - I .O e/,&) approximately 0.6 A from the nietal along the Rh-P bond R h P ? ( C l ~ t l ~ i Ounits 3 ) in the CCII: the measured density is 1.28 (2) vectors, The atomic positional and thcriiial pnr:imcters arc listed in g/cm3 (flotntion in aqueous ZnCI?). The crystals are colorless plates Tablc IV and interatomic distances and anplcs i n Table V . A list of IOIF,,I vs. IOIF,I and a table of hydrogen atom positions are availwith inajor faces of the form [loo\and uith irregular cdges. Although 1111: compound is stablc in air for ;it Icust several days. the crbstnls used able.?'
RH
0.239811 I 1 0 I
0.0778861141
0.197990 1101
11.2017)
11.741121
1 1 . 1 2 I 71
0.79171
4.66151
-0.6817I
PI11
o.
0.272392l47)
0.214311135l
12.511221
13.07137)
12.19122l
0.24123l
5.33118l
-0.07123l
PI21
0 ~ 3 0 8 7 1 8 1 3 6 ) -0.111265140)
0.20939813bl
14.49123)
12.33I~Zl
c 1111 c I141
0.235741141
0.336591141
-1.841941
0.40380116l
16.281911 25.61121
-1.20 I 9 0 I
-11.61 1 3 1
Cl15l
O.24186117I
O.48OObl2ll
0 a 3 4 1 9 2 I 16 I
31.11121
Cl12l
0~06076114)
0.26915119)
0.17992llbI
12.38 I 8 4 I
19.2115l
17.61191)
Cllbl
0.015851161
0.393341211
0.18267117l
17.821971
26.3117)
26.31111
Cl17l
0.037041
0.17398121l
0~23905116)
18.231911
30.01181
26~OlllI
Cl13l
0.20309115l
0.39227119)
0 0 1365 2 I 1 5 1
20.26196)
15.0115)
17.031931
Cll8l
0.30484116)
0.39598 122)
0.15036117)
2 2 . 1 I111
37.81201
29.0112l
2.60 123 I -0.34195l 11.0113l -3.7112l 0 . 4 9 194 I 5.91101 -2.7111 1 - 0 . 5 8 195 I -6.7111)
5.85118) 6.221751
0.3e967117)
0.340271191 0.28560 1 2 5 )
14.20 1371 18.7115) 52.11241 20.81111
c I191
0.139421171
0.373191211
0.03119116l
29.21111
24.8117l
16.47198)
0.9112l
c I211
0.38667117)
-0.16316121l
0 . 3 3 1 0 5 1151
27.51111
32.1118l
14.481961
14.5112l
0.951881 5.801 851
4.OIlll 5.21 I l l
0.37913117l
-1.54 14)
1 a e o 7 0 I 35.1
is)
13.16189) 16.5110)
19.91101
O.bl(23)
10.611 9 2 )
- 6 . 5 1 111
6.051721
-2.62198l
9.52186)
-1.lllll
13.121881
-1.81111
10.08179l 1 5 . 5 1 1 951
Z.41195I .?.dl 121
CIZ4l
0.468711181
12.41151
-2.711 881
0.395301181
25.2llZl 5 4 . 5 1181
16.511Ol
0.33621l221
-0.07510127l -0.182451271
68.9126)
c 1251
51.51251
21.91lZl
15.9117)
1 9 . 5 I 12 I
Cl22l
n.
3.3ic51i4)
-0.11967 I 2 0 I
0.14090 I 1 4 1
13.051851
26.01161
16.301921
C 1261
0.44356l15)
-0.23397122l
0.162931161
17.331911
34.0118)
23.11111
7.1111)
Cl27l Clt3l
0 . 4 3 8 3 8 I1,6 1
0.145191181
18.5110l
-1. S l l l l
0.16308116)
19.21196)
54.81191 16.8116l
30.7112l
O.23006115)
-0.00 166 I 2 2 1 -0.247481191
24e8110)
-0.93198)
c 1281
0~19569116l
-0.26638122l
0.05567 I r 7 l
22.71111
23.9117)
28.0111)
ClZ9l
0.145521171
-5.237501231
0.187581191
Z6.5li2l
28.5119)
48.41151
Clll
0.125731141
0.05146I18)
0.018641141
15.581811
14.21188)
0.911871
0111
0 . 2 0 7 6 4 l IO I
0.08649113l
0.03865 I 1 0 1
15.211 65)
lt.6115l 22.7f12)
15.46166l
-1.331731
6 . 7 2 1 541
-0.52 1741
0 121
0.02826(13)
0.08359719e.l
13.40163)
20.6111)
1 3 , 2 4 1 661
-2.05(70l
6 . 0 2 1 531
-1.39170)
0131
0.097505196l 0.06777Ill~
0.03883116)
-0.07206111l
14.71011
42.91141
13.241681
-4.12181l
4.431571
-1.2418Ol
HlllRM
0.33171191
0.1162126)
0.2537119l
2.zo1571
HIPIRH
0.2457120)
0.t419128)
0.292EIZOl
2.01(67)
nil1013
0.0170128)
0 . 0 2 3 5 ( 391
-0.07591271
* . * I . * ...~ ..........
1.021981
7 . 1 3 1 741 8.76184)
11* 41 141
-0.91 1 0 1
-3.51121
12.831951 12.431831
-1.31111
2.7llZl
-5,71111
6.65191)
-7.01121
3.01121
24.8 1111 5.4n173)
8.71141 -0.3c1881
~~*.~....~......~~*.~...~.~..~....~.........~....~......~. 3.911Ol
(’ Estimated standard deviations i n the least significant figure(s) are given in parentheses in this and all subsequent tables. The form of the 2 B 2 3 k / ) ] . The quantities given in the table are anisotropic thermal ellipsoid is: exp[-(BI I/?’+ B22k2 8331’ 2B12hX 2B13hI the thermal coefficients X IO4.
+
+
Results and Discussion Description of the Structure. As can be seen from a drawing of the inner coordination sphere, Figure I , the molecular structure of RhH?(O?COH)(P(i-Pr)3)2consists of a distorted octahedral Rh(ll1) center, with no imposed symmetry but a local point-group symmetry close to C2( (n7m). Modest hydrogen bonding between bicarbonato groups ( 0 - H - 0 = 2.65 A) couples molecules in the crystal, as illustrated in the packing diagram (Figure 2). Each hydrogen-bonded dimer possesses crystallographic inversion center, with overall symmetry of the dimer approaching C?/? (2/m). Rhodium-phosphorus bond lengths of 2.321 (2) and 2.302 (2) A are slightly shorter than other Rh - P distances recently reported for triisopropylphosphine rhodium complexes RhCI(L)(P(i-Pr),)? ( L = 0 2 , N?, CH?=CH?) (2.348-2.363 A).33 The rhodium-oxygen distances (2.279 (2), 2.306 (2) A) are very long compared with other R h - 0 distances, for instance, in acetonylacetate complexes (1.97-2.08 A)34-3hand the related carbonato complex Rh?(CO3)(PPh3)5” (2.12 A). This lengthening may result from the influence of the two trans hydride ligands. Rhodium-oxygen distances of 2.23 8, have been found trans to ortho-metalated phenyl rings.37 Distances within the 0’coordinated bicarbonato ligand are similar to those in transPdMe(v1-02COH)(PMe3)2,?1 M(OC0.H) ( M = Na,j” K41)), and related transition-metal carbonate compounds.2?,24Jx The rhodium-hydride distances found i n this complex ( a v I .44 ( 5 ) A) are shorter than typical metal-hydride bond distances of 1.5-1.7 and are close to the Rh-H distance (1.48 A) reported in an earlier structure.42 While metal-hydride distances are determined with limited accuracy by X-ray methods,43.44the trends in the published data are for Rh( 111)hydride distances to be short ( I .48 1.37 (8) A;451.41 (3), I .47 (3) A in the present study) and for Rh(l)-hydride dislances to be more nearly normal ( I .6 ( I),4J 1.66 ( 5 ) This may reflect a shift in electron density from the “hydride” n u cleus toward a Rh(lll) center, relative to a Rh(1) center.
+
+
Table V. Selected Bond Distances
( A ) and Angles (deg) i n
RhH2(O?COH)(P(i-Pr),)z Kh-P(I) R h - P( 7) Rh- O( I ) K h-O( 2 ) Rh-H( 1 ) R h H (2) Rh -H(av) C ( I )bo(I ) C(I)-0(2) C( 1)-0(3) 0(3)-H(1)0(3) O ( 3 ) .* dO(2)’ I’( I ) - C ( I I ) P( I ) - C( I 2) P( I ) - C ( 13) P(Z)-C(ZI) P(7)-C(22) l’(2)-C(23) -
P-c ;1v
C(Il)-C(14) C( I I ) - C ( 15) C( I 2 ) - C ( 16) C ( I2)-C( 17) C ( I3)-C( I X ) C(i3)-C(19)
2.321 ( 2 ) 2.302 (2) 2.306 (3) 2.279 (2) I .41 (3) I .47 (3) I .44 ( 4 ) 1.261 ( 3 ) “ 1.284 (3) 1.329 (3) 0.80 ( 4 ) 2.649 ( 4 ) 1.876 (3) 1.859 ( 3 ) 1.857 (2) 1.861 (3) 1.863 ( 2 ) 1.877 (3) 1.865 (9) 1.538 (3) 1.525 (3) 1.536 ( 3 ) 1.529 ( 3 ) 1.534 (3) I.535(3)
C(ZI)-C(24) 1.535 ( 4 ) C(ZI)-C(25) 1.527 ( 4 ) C(22)-C(26) 1.534 ( 4 ) C(22)-C(27) 1.537 (3) C(23)-C(ZX) 1.535 (4) C(23)-C(29) 1.538 (3) C-C (LIV) 1.533 ( 5 ) 169.93 (2) P(I)-Rh-P(2) 57.91 (7) O(1) - R h - 0 ( 2 ) H(I)-Rh-H(2) 81 (2) O(1)--Rh-H(1) I11 ( I ) 0(2)--Rh-H(2) IlO(1) O(I)--Rh-P(1) 98.52 ( 4 ) 0(2)--Rh-P(I) 91.22 (6) O( I)--Rh-P(Z) 90.34 (4) 0(2)--Rh-P(2) 97.57 ( 6 ) O(1) -C(I)-O(2) 121.5 ( 2 ) O(I)~C(1)-0(3) 118.7 ( 2 ) O(2) C ( 1 ) - 0 ( 3 ) 1 19.8 ( 2 ) H(1)0(3)--0(3)--C(I) 109(3)
The value in parentheses is thc standard deviation of ;I single o b s m a t i o n and is the larger 01‘ that c ~ t i m a t c dfrom the aver;!gc standnrd deviation of the individuLil obscrvations or on the assumption 11iat the v;ilues averaged arc from the s;iiiic population. If
Synthesis and Spectra of RhHZ(02COH)Lz(1, L = P(i-Pr)3; 2, L = PPh(t-Bu)z; 3, L = P(c-ChH11)3). Reaction of RhH(P(i-Pr).i)x with CO? in dry n-hexane under ambient conditions of teniperature and pressure affords a dihydrido bicarbonato compound RhH?(O?COH)(P(i-Pr)?)? ( I ) in 48%
4216
Journal of the American Chemical Society
1 101:15 1 July 18, 1979
Figure 2. Stereoscopic view of the unit cell contents of RhH2(02COH)(P(i-Pr)3)*, Alkyl hydrogen atoms are included with an artificial B of I .O A2. The view is down t h e y axis, with the x axis across the page. At the center of each drawing is the inversion center which serves as the coordinate origin for Table IV
Scheme I yield. A PPh(t-Bu)z analogue 2 was obtained in 17Yo yield from R h H ( CO, )Lo a similar reaction of CO, with RhH(N2)(PPh(t-Bu)l)l. The T formation of these dihydrido bicarbonato compounds was totally unexpected; in fact, we originally formulated them as Rh( 1)hydrido formato carbon dioxide complexes, and their correct formucomplexes lation was the result of the X-ray analysis of 1. Traces of water, present as an impurity in the COz gas, are most probably responsible for their formation. When water was deliberately added to the reaction mixture the yield of the dihydrido bicarbonato complexes was dramatically improved to 85% for 1 (see Experimental Section). The dihydrido bicarbonato compounds 1-3 are obtained as undergoes nucleophilic attack by H 2 0 at the coordinated CO2 colorless crystals which are stable in air for several days. ‘ H group. Several attempts were made to detect or isolate a C O ? N MR spectra of 1 and 2 show a hydride signal as a doublet of complex by treating RhH(P(i-Pr)3)3with CO2, carefully dried triplets resulting from coupling with two equivalent phosphorus with molecular sieves, in dry n-hexane. All attempts failed. and nuclei and the rhodium nucleus, and a broad bicarbonato the only compound observed (except for unreacted starting proton signal (Table 11). The methyl proton signal of the material) was 1 in trace amounts. (2) The Rh(l) hydride phosphine ligands in 1 and 2 is split into a quartet and triplet, complexes may oxidatively add H-CO3, formed by the reaction respectively, owing to virtual coupling. Thus the IH N M R data of CO? with H20. (3) Water may be oxidatively added by the are consistent with a stereochemical assignment of cis hydrido Rh( I ) hydride complexes. The compound RhH( P(i-Pr)j)3 ligands and trans phosphine ligands as found in the X-ray readily adds water at room temperature in aqueous pyridine analysis of 1 (Figure I ) . Poor solubility of the P(c-ChH11)j to give an ion pair dihydrido hydroxy complex [RhHr(py),(P(i-Pr)j)z][OH]; the cation may be isolated as the BPh4analogue 3 prevented observation of either the hydrido or the bicarbonato proton signals, but the compound was unequivosalt.jxThe apparent pH of [RhH2(py)l(P(i-Pr)3)?][ O H ] incally characterized by its infrared spectrum (Table I). dicates that the system is more basic than N a O H in aqueous pyridine. Therefore, a facile formation of the bicarbonate anion Infrared spectra of 1-3 show two vibrations assignable to from OH- and C o r would be expected. Routes 2 and 3 appear V R h H in the region 21 20-2220 cm-I. Interestingly, when 3 is to be more likely than I ; which route dominates may depend recrystallized from toluene the Rh-H IR stretching frequencies (2138, 2158 cm-l) are different from those observed on the pH and Rh:H?O:C02 ratio. (21 IO, 2160 cm-’) when 3 is precipitated from T H F . The Formation of RhH2(02CH)L2 (4, L = P(i-Pr)3; 5, L = OzCOH vibrations (Table I ) resemble those of the known biP(c-C6HlI)3).Since facile insertion of COz into transition metal-hydride bonds has been amply documented,’ ‘ I it carbonato dimer dianion (HC03)2?- of point-group symmetry C ~ I ,In. the ~ ~bicarbonato complexes 1-3 VC==O is a t lower is rather surprising that these Rh( I ) hydride complexes react frequency than V ~ = Oof trans-PdMe(q1-02COH)(PMe3)2with C o r to form instead the dihydrido bicarbonato complexes and of (HC03)2z-, and this shift is consistent with q2-bicar1 and 3, even under ostensibly anhydrous conditions. Despite bonato coordination in 1-3. The low value of vo b{ (2649-2660 careful searching we have been unable to detect the expected insertion product, a formato complex. in the reaction of RhH L3 cm-I) of 1-3 is a manifestation of hydrogen bonding between with CO2. Therefore formato complexes were prepared sepabicarbonato ligands. From the correlation between V O H and rately to examine their chemical behavior. 0 - H - - -0distances in several hydrogen-bonded dimers,47 an Formato complexes RhH?(O2CH)L2(4, L = P(i-Pr)j; 5 , 0 - H - - -0distance of 2.65 A for the dimeric complexes 1-3 L = P(c-C6H I 1 ) 3 ) could be obtained as stable, colorless crystals is calculated. This value agrees remarkably well with the disby treating the Rh(l) hydride complexes with formic acid. The tance found in 1 (2.649 (4) A). That the hydrogen bonding compounds 4 and 5 are stable in air in the solid state. and i n persists in benzene solution is shown by a cryoscopic molecular solution they do not evolve H2 a t room temperature. The ‘ H weight determination of 1 (observed 793, required for dimer N M R spectra (Table I I ) of 4 and 5 suggest that the two h y 973 amu). drido and the two phosphine ligands arc mutually cis and trans. Formation of RhH2(02COH)L2 Complexes. Three possible respectively, and these compounds are probably structurally pathways for the formation of the dihydrido bicarbonato vcry similar to 1. complexes from the Rh( I ) hydride complexes are depicted i n Interestingly, the two hydrido hydrogen nuclei couple with Scheme I . the formato proton across the four intervening bonds. The ( I ) A Rh-CO? complex may be formed hhich subsequently
Ihers. Otsuka, et ai.
/
4217
R h o d i u m Bicarbonate and Formate Complexes
Scheme U hydrido resonance of 4 is observed as two sets of double triplets (‘JI, 11 = l.I.Jl1 Kh=28.8,Jl{ I , = 18,OHz),andtheformato proton signal consists of seven slightly broadened lines (4./Jt{ 11 = I . I , ? J I I K h = 2.0, 4 J ~ , = 1 Hz). The P ( c - C ~ H1I) 3 analogue 5 shows a similar long-range coupling between the hydrido and formato hydrogen nuclei ( j J l + ~= 1.0 Hz). A related dithioformato Ir complex IrH,(S?CH)(PPh3)2 also has ;I long-range coupling j J I { 14 = 1.5 Hz.49Observation of Wtype long-range coupling suggests that the RhH,(O?CH) moiety in 4 and 5 is planar.5o Two Rh-H stretching bands are observed in the IR spectra of 4 (2130.2145cm-I) and 5 (21 I4,2140cm-’) and indicate that the hydrido ligands are cis, again as in the dihydrido bicarbonato complexes 1 and 3. The formato ligands or4 and 5 give rise to vibrational bands at 1560 and 13 I O , and 1555 and I3 I O cm-’. respectively. These values are comparable with those reported for RuH(02CH)(PPh3)3(1553, 1310 cm-’)” OC-Rh-0,COH (L = P(i.Prj3) and trans-PtH(O:CH)(P(i-Pr)3)2 (1530, 1310 cm-’).Il Formation of Rh(02COH)(CO)L2(6, L = P(c-C6H~1h; 7, L L = P( i-Pr)3)and Rh2(02CO)(C0)2(P(i-Pr)3)j (8). Carbonyl bi6 , L = P(c-C,H,,), carbonato ( 6 , 7 ) and carbonyl formato (9,lO)complexes were 7, L = P(i-Pr)3 obtained, at first totally unexpectedly, from the reaction of the corresponding dihydrido complexes with carbon dioxide. The bicarbonato compounds are also involved in the mechanism of the catalysis of the water-gas shift reaction by the Rh( I ) L hydride complexes.” Here we report details of their prepaI ration, their spectral data. and their subsequent reactions. OC-Rh-OH The carbonyl bicarbonato complexes may be prepared by three separate routes, summarized in Scheme I I . The dihydrido L bicarbonato complexes 1 and 3 reduce CO1 to give the carbonyl bicarbonato complexes and H 2 0 (discussed below). Alternatively, the dihydrido bicarbonato complexes may be treated temperature IH N M R spectrum indicates equivalence of all with CO to form the carbonyl bicarbonato complexes and Hr. four P(i-Pr)1 ligands. Equivalence of all four phosphorus nuclei A third, totally independent method of synthesizing the caris also seen in the low-temperature j l P N M R spectrum ( J p - ~ l , bonyl bicarbonato complexes is from the reaction of the cor= 129.6 Hz, 6 53.8 ppm downfield from H3P04; -55 O C in responding carbonyl hydroxy compounds with CO2. Spectral toluene). The room-temperature and high-temperature ”‘P data and melting point determinations prove that these diverse N M R spectra are complicated, with broad lines and the appreparative methods give identical products. pearance of free phosphine. One interpretation of the N M R Because of very limited solubility and a reversible decardata is that the bridging carbonato ligand is q l - v l at low boxylation (vide infra) our attempts to detect the bicarbonato temperature but rapidly loses phosphine and equilibrates with hydrogen N M R signal of Rh(CO)(O2COH)( P(c-C6H I ] ) 3 ) 2 a VI-$ structure at higher temperatures, eq I . The I R spec(6) have failed. However, the P(i-Pr)3 analogue 7 is readily soluble in organic solvents and can be characterized by IH L L N M R spectroscopy (Table 1 1 ) . The IR spectrum of 6 shows a strong absorption from the coordinated CO molecule at 1942 OC-Rh-0-C-0-Rh-CO cm-’ and several bands from the bicarbonato ligand (Table II I ) . Upon deuteration, the bands from U O - H and 6 0 ~ 0are 0 L L shifted from 2650 to 2087 and from 1420 to 1062 cm-I, respectively, while the coupled vibration v ~ - 0 uc-0 60~0 8 is shifted from I355 up to 1405 cm-l. The trends are consistent with those observed for the bicarbonato dimer d i a n i ~ (Table n~~ L I). The VC=O band also shifts markedly upon deuteration ( 1608 to 1590 cm-I). These data indicate strong 0-H hydrogen bonding in 6, and it is likely that both 6 and 7 form hydrogen-bonded dimers similar to 1.” While the P(c-C6H11)3complex 6 is stable at room temperature, the P(i-Pr)3 analogue 7 readily forms the binuclear trum of 8 has bands arising from the carbonato ligand at I533 carbonato complex 8 with the evolution of CO1. The formation s, 1300 s, 1275 s, and 829 w cm-l, which differ significantly of 7 has been confirmed by ‘ H N M R and IR spectra (Tables from those of known q1-q2 bridging carbonato complexes I and I I ) but its instability has prevented the isolation of an Rh2(02CO)(PPh3)5 (1485, 1460, 1350, 820 ern-')" and analytically pure sample. Attempts to recrystallize 7 result in Mo2(C0)2(0+20)2(PMe?Ph)6 ( I 835 cm-1),24and from those the formation of 8. Compound 8 is also obtained from the reof a mononuclear $carbonate Pt(02CO)(PPh3)2 ( 1680, 1180, action of CO2 with 1 in pyridine, although 7 is probably a 8 15 cm-1).23The strong ucf0 band of 8 ( 1 934 cm-l) with a shoulder (1 950 cm-I) is consistent with q l - q l coordination, transient intermediate. The ‘ H N M R spectrum of 8 measured at room temperature shows two broad signals centered a t 6 1.24 as t w o strong UC=O bonds would be expected for q7’-q2coorand 2.27. which are assignable to the CH1 and C H protons of dination. Formation of the binuclear carbonato complex 8 from P(i-Pr)3. On cooling the sample to -10 OC the methyl proton two molecules of the bicarbonato complex 7 most likely prosignal was observed at 6 1.26 as a quartet ( 3 J ~ - + p 5 J p~ = ceeds via intermolecular oxidative addition of the bicarbonato 0 - H group, followed by reductive elimination of HzC03 (eq 13.4, J H 14 = 6.7 Hz) owing to virtual coupling. The lowI)
I I
I
I I
+
+
I I
4218
Journal of the American Chemical Society
1 101:15 /
July 18, 1979
L
I I L
RhHL,
1gpd
2 OC-Rh-O,COH
RhH,(O,COH)L,
7
-
L
L
=
P(i.Pr)3(l)
+
L
L = PPh,
i
L
I
OC-Rh-0,CO-Rh-CO
I
L
I
I
+
HPCO.] ( 2 )
L 8 I,
L
L
I I L\Rh/O\ C-0-Rh-L I 2). We confirmed the evolution of 0.45 mol of CO? per mol of C~Rh--OCO.--Rh-CO (8) 7. I I L/ \J I The relative stability of 6 we explain by the steric bulk of L L L P ( c - C ~ H I(cone ~ ) ~ angle” 1 7 0 O ; compare P(i-Pr)3, cone angle presence of water, is the formation of RhH2(0,COH)L2. The 160’) which prevents the bimolecular reaction of 6.When difference in steric bulk of the phosphine ligands determines heated in T H F, however, 6 undergoes decarboxylation to give the stability of the dihydride coordination i n RhH2Rh(OH)(CO)(P(c-ChHI 1 ) 3 ) 2 ( q - 0 1927, I’OH 3600 cm-I) ( 0 2 C O H ) L l and thereby the course of the subsequent reactogether with an uncharacterized carbonyl-containing comtions. The Rh-H stretching frequencies and, presumably, the pound ( V C O 1945 cm-I). The reverse reaction, insertion of CO? strength of the Rh-H bond decrease w3ith a decrease in the cone into the Rh-OH bond of Rh(OH)(CO)(P(c-C6H I 1)3)2,occurs angle of the phosphine, PPh(t-Bu)? (cone angle--170’ 5 h ) 1 readily at room temperature to regenerate 6. Reversible deP(c-C6H I 1); ( 1 70’ .52) > P(i-Pr)x ( 1 60’ 5 2 ) (see Table I ) . A carboxylation is also suggested by the exchange of ”C-bicarsimilar trend was found for the Rh-H stretching frequencies bonate for ’;C-bicarbonate under ’C02 (see Experimental of RhHZCIL2. L = P(f-Bu)34S (cone angle 182” S 2 ) , P(cSection). Similar decarboxylation reactions are known for a cobalt bicarbonato complex53 and for a l k y l c a r b o n a t ~ , ~ ~CbHl . ~ ~ 1)3,59 PPh,hD( 1 4 5 O ) , where the dihydride coordination of the P(t-Bu)3 complex is stable but that of the PPh? analogue carbamato,I6 and format^^^^' complexes. is reversible. A facile reductive elimination of Hz from Formation of the analogous bicarbonato complex with triRhHz(02COH)(PPh3): can therefore be postulated, resulting phenylphosphine, Rh(CO)(O2COH)(PPh3)2, from the reaction of Rh(OH)(CO)(PPh3)2 with CO2 has been reported.56 in Rh(O>COH)(PPh3)? which subsequently forms the carbonato complex through a bimolecular oxidative addition of Interestingly, the reported IR spectrum of this complex (1977 the bicarbonato OH bond. I n contrast, the dihydride coordis, 1655 s, 1368 s, 1290 s, 1083 m cm-l) differs significantly nation in RhH2(02COH)L2 (1, L = P(i-Pr);; 2, L = PPh(tfrom the spectra of 6 and 7 (Table I). A supposed carbon B u ) ~ 3, ; L = P ( c - C ~ Hi)3) I is stable toward reductive elimidioxide complex, R h ( 0 H ) (CO) (COz) (PPh3) 2,57 has a specnation and instead reduces COz to give Rh(C0)(02COH)L2. trum ( I 966 vs, 1620 s, 135 1 s, 821 s cm-’) much more closely For L = P(i-Pr)3 dimerization occurs to give the carbonato resembling those of 6 and 7 (Table I ) . We have reexamined complex 8. these complexes and believe that the “carbon dioxide” complex Formation of Rh(C0)(02CH)L*(9, L = P(i-Prh; 10, L = is actually the bicarbonato complex, and the reported “bicarP(c-C6H11)3).Both 9 and 10 may be obtained in high yield from bonato” complex is actually an alcoholate, possibly the ethyl the reaction of CO2 with the corresponding dihydrido formato carbonato complex Rh(C0)(02COC2Hs)(PPh1)2. formed from the reaction of the genuine bicarbonato complex with alcohol (the solvent). In support of this postulate, treating Rh(CO)(OlCOH)(PPh3)2 with different alcohols (methanol, ethanol, 2-propanol) gives complexes with noticeably different IR spectra. The IR spectrum of the product obtained from the L reaction with ethanol is identical with that reporteds6 for the 4,5 “bicarbonato” complex. In nonalcoholic solvents or a t elevated temperatures these complexes are unstable and tend to decompose, resulting in what is believed to be a dimeric complex,5h and we have not been able to obtain analytically pure samples nor reliable ’ H N M R data for any of these hypothetical alcoholates. A reaction closely related to the present ones is the formation of a carbonato complex Rh2(02CO)(PPh3)5 from L RhH(PPh3), ( n = 3, 4) and free C 0 2 . Both H20 and COz -H,O have been suggested as possible sources of the carbonato liOC-Rh--02CH (3) gand, but no mechanistic aspects were reported.22 The formation of Rh2(02CO)(PPh3)5 may involve a sequence of steps L similar to those in the formation of Rh2(CO)2(02CO)(P(iPr)3)4 (8) (see Scheme 111). In both cases the first step, in the 9,lO
-
I
1
Ibers, Otsuka, et al.
/ Rhodium Bicarbonate and Formate Complexes
complexes 4 and 5 . Compound 9 may also be obtained from the direct reaction of RhH(P(i-Pr)3)3 with 2 equiv of formic acid a t room temperature, with evolution of H2. This direct method is less effective for the preparation of 10. Treating Rh2H2(p-N2)(P(c-ChH1I ) ~ ) with J a large excess of formic acid gives 10 as a minor product, the major product being the dihydrido formato complex 5. This result suggests the dihydrido formato complexes 4 and 5 are intermediates in the formation of Rh(CO)(O?CH)L? (9 and 10) from RhHL3 or Rh>H?(p-N?)Ldand excess formic acid. The reaction may proceed via reductive elimination of H2 from the dihydrido formato complexes and subsequent oxidative addition of HCOzH by the transitory species Rh(OZCH)L2 (see eq 3). The bulkier phosphine P(c-ChH I I ) ) ~ ?is expected to stabilize the dihydride coordination and to inhibit the loss of Hz to form Rh(02CH)L2, relative to the P(i-Pr)3 analogue. These carbonyl formato complexes are crystalline, yellow compounds, stable i n air for a few days. The IR spectrum of 9 exhibits three characteristic bands assignable as U C O ( 1 954 cm-I) and uo2c(asym 1633, sym 1310 crn-'). Corresponding bands of 10 are observed at 1945, 1630, and 1292 cm-I. I n comparison with literature values for PtH(q1-02CH)(P(cChHl 1)3)2 (1620 cm-')Ioand RuH(vz-02CH)(PPh3)3 (1553 ~ m - ' ) ~the ] relatively high frequency of uoZc (asym) of Rh(CO)(O?CH)L? may be indicative of coordination of the formato ligand. The dihydrido formato complexes 4 and 5 , also with $-formato coordination, have IR absorptions at 1560 and 13 I O cm-'. Observation of virtual coupling in the methyl IH N M R spectrum (see Table I I ) again suggests a trans configuration of the phosphine ligands of 9. Reduction of Carbon Dioxide. The facile reduction of CO. to C O by dihydrido Rh(Il1) complexes, here the dihydrido bicarbonato complex 3, to give H 2 0 and the carbonyl bicarbonato complex 6 (see eq 4), is a novel and potentially useful
L HI.I
I
o
/' \
COH
+ CO,
L 3
-
L
H,O
I
+ OC-Rh-02COH
I
(4)
L 6
reaction that has received very little attention. To the best of our knowledge the only previous reports of similar reactions are the reaction of RhCI(PPh3)3 with Hz and C 0 2 a t high pressure and 100 O C to give RhCI(CO)(PPh3)220 and the formation of RhCI(CO)(PPh3)2 from RhCIH(Si(OEt)3)(PPh3)2 and C O Z .The ~ ~ reverse reaction, the formation of H2 and C 0 2 from H20 and CO, is the well-known water-gas shift reaction. Since the water-gas shift reaction is thermodynamically favorable and is readily catalyzed by Rh( [)-hydride c o r n p l e x e ~ ,it~ ~is very surprising that the formation of a Rh( 1)-carbonyl complex from C02 and a Rh( Ill)-dihydride complex is also thermodynamically favorable. We therefore examined the reaction carefully to prove that it does indeed proceed as in eq 4. 1. The metal complexes involved have been well characterized. The starting complex RhH2(02COH)(P(c-ChH I 1)3)2 (3), both by its IR spectrum and by its method of preparation, is analogous to RhHz(OZCOH)(P(i-Pr)3)2 ( l ) ,which has in turn been characterized by diffraction methods. In fact, 1 itself reacts with C02 in a similar fashion but the initial bicarbonato complex 7 is unstable and subsequently dimerizes to form 8. The metal-containing product, the carbonyl bicarbonato Rh( I )
4219
complex, has been characterized spectroscopically and synthesized by independent methods. 2. The water formed in the reaction has been detected by VPC analysis of the reaction mixture. 3. Reaction of with the dihydrido bicarbonatocomplex 3 gives the 13C-labeledcarbonyl bicarbonato complex (see Experimental Section). This rules out the possibility that the rhodium carbonyl product might have been formed from traces of CO in the "CO2" or alcohols in the solvent. 4. The IR spectrum of the reaction residue shows no absorption bands ascribable to free or coordinated phosphine oxide.h2Combined with the observation of near-quantitative yields'" this eliminates the possibility of an oxygen atom transfer from COz to PR3.8.h3 5. The dihydrido formato complexes 4 and 5 react with CO? in an exactly analogous manner. Reacting 4 with CO2 i n pyridine affords Rh(C0)(02CH)(P(i-Pr);)? (9) together with a sniall amount of 8. VPC analysis of the reaction mixture shows the quantitative formation of water, and H2 was not detected in the vapor phase. While facile reduction of CO-, by 3 occurs in pyridine, the reduction does not occur in toluene or T H F . This may simply reflect the very limited solubility of 3 in these solvents at room temperature. The compound Rh?H?(p-N?)(P(c-ChH1 I ) ~ ) J in THF-H?O reduces CO2 when treated with excess amounts, probably via the initial formation of 3 which in turn reacts with excess CO2 before precipitating. The IR spectrum of the solid residue obtained upon evaporating a pyridine solution of 3 shows UC=O a t 1695 cm-I, a considerable shift from V C = O of 3 itself ( 1 585 cm-I), and the uOt4 band can no longer be found. This suggests that the 7'-bicarbonato ligand in 3 may be converted to coordination upon attachment of pyridine. A second explanation is that pyridine disrupts the probable hydrogen-bonded dimeric structure of 3. A third possibility is that pyridine displaces the bicarbonato ligand entirely to form [RhH2(py)2(P(c-CbHlI)3)21[O2COH1. The mechanism of COz reduction by the dihydrido bicarbonato complexes 1 and 3 probably proceeds by CO2 insertion into the Rh-H bond, leading to either a hydroxycarbonyl species RhH(C02H)(02COH)Ll or a formate complex RhH(02CH)(02COH)L>. Elimination of water completes the reaction. Generally, insertion of C O ? into a transition metal-hydride bond gives a formato c o m p l e ~ ~ I- I~although .~formation of a hydroxycarbonyl complex has been reported.64 We cannot distinguish between the two possible intermediates RhH(CO?H)(O2COH)L2 and RhH(02CH)(02COH)L2 from our present data, but the hydroxycarbonyl complex is the more intuitively appealing. There are also two possible modes for the oxidative addition of H C 0 2 H to the hypothetical intermediate species Rh(02CH)L2, leading to either RhH(CO?H)(02CH)L2 or RhH(02CH)2L2. Again elimination of water completes the reaction to form Rh(C0)(02CH)L2. Here also the literature contains reports of both possible intermediates. The C-H fission of HCOzH accounts for the formation of a hydroxycarbony1 species Ir-COzH in the reaction of IrCIjL3 with formic acid.h5 Decarbonylation of hydroxycarbonyl species has been observed, for example, in the formation of trans-PtCl(C0)(PEt3)2 from PtCI(CO*H)( PEt3)2,6h and is postulated for oxygen exchange reactions of metal carbonyls with H2180.h7h9 The usual reaction of formate complexes is decarboxylation to give free COz and metal hydride complexes.lO,l 1.51.70 If such a process were occurring rapidly in the reaction of Rh(02CH)Lz with formic acid, the net result would be the catalytic decomposition of HCO2H into H2 and COz with restoration of the dihydrido formato complex RhH2(02CH)L2. Since the CO2 thus formed would rapidly react with RhH2(02CH)L2, we again cannot distinguish between the possible intermediates from our present data.
4220
Journal of the American Chemical Society
Summary and Conclusions Rh( I)-hydride complexes with bulky phosphine ligands have been found to react with C02 and HzO to form dihydrido bicarbonato Rh(ll1) complexes; no reaction occurs if water is excluded. Similar dihydrido formato complexes are formed when the Rh(1)-hydride complexes react with formic acid. These dihydrido Rh(l1l) compounds will react further with CO2, CO, or excess formic acid to form Rh(1) carbonyl complexes. W e had hoped that studies of the formato complexes would provide some mechanistic information on the reaction of the rhodium dihydride complexes with C o r , but the formate complexes studied here behave so similarly to the rhodiumhydride-carbon dioxide systems that obvious mechanistic information was not obtained. The formation of Rh(CO)(OrCOH)L2 and HzO from RhH2(02COH)L2 and COr
COr
+ RhH2(02COH)L2
+
H20 Rh(CO)(O2COH)L2
+
(5)
is, a t first glance, the reverse of the water-gas shift reaction" HrO
+ CO
-
Cor
+ H2;
AH2980~
= -9.85 kcal/mol, -41.2 kJ/mol
K , = 40.4 (6) and should therefore be thermodynamically unfavorable. In retrospect, however, the driving force for the reduction of CO, is seen to be the formation of the Rh(1)-carbonyl b0nd.j It can easily be shown that the reduction of CO2 (eq 5 ) is thermodynamically favorable, even with the knowledge that the water-gas shift reaction (eq 6) is also favored, if the direct reaction with free CO
CO
+ RhH2(02COH)L2
-+ H2
Rh(CO)(O2COH)L2
(7)
is favorable. This has been demonstrated for 1, L = P(i-Pr)l.
Acknowledgments. This work was funded in part by the Japan Society for the Promotion of Science and the U S . N a tional Science Foundation through the Japan-U.S. Cooperative Science Program (GR021/INT77-07152) and by N S F Grant CHE76-10335. D.L.T. acknowledges support from the National Science Foundation through a National Needs Postdoctoral Fellowship. H e also thanks the Osaka group for their hospitality. Supplementary Material Available: A l i s t of 101F,I vs. 101F,I and a table of hydrogen atom positions (41 pages). Ordering information is given on any current masthead page.
References and Notes (1) (a) Osaka University. (b) Northwestern University. (2) Vol'pin. M. E.; Kolomnikov, I. S. "Organometallic Reactions", Vol. 5; Wiley-lnterscience: New York, 1975, p 313-386. (3) Ito. T.; Yamamoto. A. J. SOC.Org. Synth. Jpn. 1976, 34, 308-318. (4) Eisenberg. R.; Hendriksen, D. E. Adv. Catal., in press. (5) Aresta, M.; Nobile, C. F.; Albano, V. G.; Forni, E.; Manassero, M. J. Chem. Soc., Chem. Commun. 1975, 636-637. Aresta, M.; Nobile, C. F. J. Chem. SOC.,Dalton Trans. 1977, 708-71 1. (6)Herskovitz, T.; Guggenberger, L. J. J . Am. Chem. Soc. 1976, 98, 16151616. (7) Miyashita. A.; Yamamoto, A. J. Organomet. Chem. 1976, 173, 187199. (8) Aresta, M.; Nobile, C. F. lnorg. Chim. Acta 1977, 24, L49-L50. (9) Komiya. S.; Yamamoto, A. Bull. Chem. Soc. Jpn. 1976, 49, 784-787. (IO) Immirzi, A.; Musco, A. lnorg. Chim. Acta 1977, 22, L35-L36. (11) Yoshida, T.; Ueda, Y.; Otsuka. S. J. Am. Chem. SOC.1978, 700,39413942. (12) English, A. D.; Herskovitz. T. J. Am. Chem. Soc. 1977, 99, 1648-1649. (13) Tsuda, T.; Chujo. Y.; Saegusa, T. J. Am. Chem. SOC.1978, 700,630-632,
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and references cited therein. (14) Ashworth. T. V.; Singleton, E. J . Chem. SOC., Chem. Commun. 1976, 204-205. (15) Chisholm, M. H.; Cotton, F. A,; Extine. M. W.; Reichert, W. W. J. Am. Chem. SOC.1978, 100, 1727-1734, and references cited therein. (16) Chisholm. M. H.; Extine, M. W. J. Am. Chem. Soc. 1977, 99, 782-792. (17) Chisholm. M. H.: Extine, M. W. J. Am. Chem. Soc. 1977, 99, 792-802. (18) Yoshida. T.; Okano. T.; Otsuka, S. J. Chem. Soc., Chem. Commun. 1978, 855-856. (19) Yoshida, T.; Otsuka, S. To be published. (20) Koinuma, H.; Yoshida, Y.; Hirai, H. Chem. Lett. 1975, 1223-1226. (21) Crutchley, R . J.;,Powell. J.; Faggiani, R.; Lock, C. J. L. lnorg. Chim. Acta 1977, 24, L15-Ll6. (22) Krogsrud, S.; Komiya, S.; Ito, T.; Ibers, J. A.; Yamamoto. A. lnorg. Chem. 1976, 75.2798-2805. (23) Hayward, P. J.; Blake, D. M.; Wilkinson, G.; Nyman, C. J. J. Am. Chem. SOC. 1970, 92, 5873-5878. (24) Chatt, J.; Kubota, M.; Leigh, G. J.; March, F. C.; Mason, R.; Yarrow, D. J. J . Chem. Soc., Chem. Commun. 1974, 1033-1034. (25) Hoffman, P. R.; Yoshida. T.; Okano, T.; Otsuka, S.: Ibers, J. A. lnorg. Chem. 1976, 75, 2462-2466. (26) Gregorio. G.; Pregaglia, G.;Ugo, R. lnorg. Chim. Acta 1969, 3 , 89-93. (27) The design of the low-temperature apparatus is from Huffman. J. C. Ph.D. Thesis, Indiana University, 1974. (28) Corfield, P. W. R.; Doedens, R . J.; Ibers, J. A. lnorg. Chem. 1967, 6, 197-204. (29) Cromer, D. T.: Waber. J. T. "International Tables for X-ray Crystallography", Vol. IV: Kynoch Press: Birmingham, England, 1974; Tables 2.2A and 2.3.1. Stewart, R . F.; Davidson, E. R . ; Simpson, W. T. J. Chem. Phys. 1965, 42, 3175-3187. Computer programs used in the data reduction and refinement include, in addition to local programs, AGNOST, the Northwestern absorption program, modified versions of Zalkin's FORDAP Fourier summation program, Busing's and Levy's ORFFE error function program, and Johnson's ORTEP plotting program. NUCLS, the full-matrix least-squares program, closely resembles the Busing-Levy ORFLS program. The diffractometer was run under the disk-oriented Vanderbilt system: Lenhert, P. G. J . Appl. Crystallogr. 1975, 8,568-570. See paragraph at end of paper regarding supplementary material. Busetto, C.; D'Alfonso, A,; Maspero. F.; Perego, G.; Zazzetta, A. J. Chem. Soc., Dalton Trans. 1977, 1828-1834. Aleksandrov, G. G.; Struchkov, Yu. T. 2. Strukt. Khim. 1970, 7 7 , 10941100. Hewitt, T. G.; DeBoer, J. J. J. Chem. SOC.A 1971, 817-822. Morrow, J. C.; Parker, Jr., E. B. Acta Crystallogr., Sect. B 1973, 29, 1145-1 146. Hoare, R . J.; Mills, 0. S. J . Chem. Soc., Dalton Trans. 1972, 21382141. Cariati. F.; Mason, R.: Robertson, G. B.; Ugo, R. Chem. Commun. 1967, 408. Sass, R. L.; Scheuerman, R. F. Acta Crystallogr. 1962, 75,77-81. Sharma, B. D. ibid. 1965, 78. 818-819. Pedersen, B. Acta Crystallogr., Sect. B 1968, 24, 478-480. Frenz, E. A.; Ibers, J. A. "Transition Metal Hydrides", Muetterties, E. L., Ed.; Marcel Dekker: New York, 1971; Chapter 3, pp 33-74. Muir, K. W.; Ibers, J. A. lnorg. Chem. 1970, 9, 440-447. Ibers, J. A. Adv. Chem. Ser. 1978, No. 767, 26-35. La Placa, S.J.; Ibers, J. A. Acta Crystallogr. 1965, 18, 511-519. Yoshida, T.; Otsuka, S.; Matsumoto, M.; Nakatsu, K. lnorg. Chim. Acta 1978, 29, L257-L259. Nakamoto, K.; Sarma, Y . A.; Ogoshi, H. J . Chem. Phys. 1965, 43, 1177-1 181. Nakamoto, K.; Margoshes, M.; Rundle, R. E. J . Am. Chem. SOC.1955, 77, 6480-6486. Yoshida, T.; Otsuka, S. To be published. Robinson, S. D.; Sahajpal, A. J. Organomet. Chem. 1975, 99, C65C67.. Jackman, L. M.; Sternhell, S. "Applications of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry" Pergamon Press: Elmsford, N.Y., 1969; p 34. Komiya, S.; Yamamoto, A. J. Organomet. Chem. 1972, 46, C58-C60. Tolman, C. A. Chem. Rev. 1977, 77,313-348. Chaffee, E.; Dasgupta, T. P.; Harris, G. M. J. Am. Chem. SOC.1973, 95, 4169-4173. Tsuda, T.; Saegusa, T. lnorg. Chem. 1972, 17, 2561-2563. Kolomnikov, I. S.; Gusev, A. I.; Aleksandrov, G. G.; Lobeeva. T. S.: Struchkov, Yu. T.; Vol'pin, M. E. J. Organomet. Chem. 1973, 59, 349351. Flynn. E. R.; Vaska. L. J. Am. Chem. Soc. 1973, 95, 5081-5083. Flynn, E. R.; Vaska, L. J. Chem. SOC., Chem. Commun. 1974, 703704. Otsuka. S.;Yoshida, T.; Matsumoto, M.; Nakatsu, K. J. Am. Chem. SOC. 1976, 98,5850-5858. Van Gaal, H. L. M.; Verlaak. J. M. J.; Posno, T. lnorg. Chim. Acta 1977, 23, 43-5 1. Osborn. J. A,: Jardine. F. H.: Younb, J. F.; Wilkinson, G. J. Chem. SOC. A 1966, 1711-1732. Svoboda, P ; Belopotagova, T. S.; Hetflejs. J. J. Organornet. Chem. 1974, 65, C37-C38. (62) Bandoli, G.; Ciemente, D. A,; Deganello, G.; Carturan. G.; Uguagliati, P.; Belluco, U. J. Organomet. Chem. 1974, 71, 125-133. (63) Ito, T.; Yamamoto, A. J. Chem. Sdc., Dalton Trans. 1975, 1398-1401. (64) Vol'pin. M. E.; Kolomnikov, I. S. Pure Appl. Chem. 1973, 33, 567-581. (65) Kolomnikov, I. S.; Kukolev, V. P.; Koreshkov, Yu. D.; Mosin. V. A,; Vol'pin, M. E. lzv. Akad. Nauk SSSR 1972, 2371.
Taura
1 Stereoselecticity in Ion-Pair Formation
(66) Dixon, K . R.; Hawke, D. J. Can. J. Chem. 1971, 49, 3252--3257. (67) Muetterties, E. L. Inorg. Chem. 1965, 4 , 1841-1842. (68) Darensbourg, D. J.: Froelich, J. A . J. Am. Chem. Soc. 1977, 99, 47264729. (69) Darensbourg, D. J.; Froelich, J. A. J. Am. Chem. SOC. 1977, 99, 5940-
4221 5946. (70) Laing, K . R.; Roper, W. R. J . Chem. SOC.A 1969, 1889-1891. (71) Thermodynamic data are taken from Campbell, J. S.: Craven, P.: Young, P. W. "Catalyst Handbook", Springer-Verlag:New York, 1970: Chapter 6, pp 97-125. and Table 5, pp 192-195.
Stereoselectivity in Ion-Pair Formation. The Contribution of the Rotamers to the Interaction of Mono- and Disubstituted Succinate Dianions with Tris( ethylenediamine)cobalt( 111)' Toshiaki Taura Contribution f r o m the Department of Chemistry, Faculty of Science, Hiroshima Unioersity, Hiroshima 730, Japan. Receii>edSeptember 19, I978
Abstract: The changes i n the circular dichroism (CD) spectra of optically active tris(ethylenediamine)cobalt(lll) have been measured upon addition of monosubstituted succinate dianions (malate, thiomalate, aspartate, methylsuccinate, phenylsuccinate, chlorosuccinate, bromosuccinate. and succinate ( - 0 O C C H z C H ( R ) C O O - ; R = O H , S H , "2, CH3, CsHs, CI, Br, and H ) ) , and upon addition of 1,2-disubstituted succinate dianions (dibromosuccinate, dimethylsuccinate, tartrate (dihydroxysuccinate), and I ,2-~yclohexanedicarboxylate (-OOCCH(R)CH(R)COO-; R = Br, CH3, and O H , and R-R = CHz(CH2)4CH2)). It is found that the resultant CD changes, which are due to the outer-sphere association with these dianions, are similar in shape and magnitude for the monosubstituted succinate dianions, while they vary depending upon the kind of two substituents R for the disubstituted succinate dianions. These findings a r e examined on the basis of the idea that the substituted succinate dianion interacts with the complex ion through the C O O - group as a mixture of their two rotamers, in which the two C O O - groups a r e gauche and trans to each other. It is, eventually, concluded that the resultant C D changes are dependent on the fractional populations of gauche and trans rotamers, and the populations of these rotamers are controlled only by the electrostatic repulsion between the two C O O - groups for the monosubstituted succinate dianions, while they are controlled by the interaction between the substituents R as well for the disubstituted succinate dianions. Furthermore, it is proposed that the conformation of the dicarboxylate dianion can be determined by the analysis of the C D change. Actually, the fractional populations of rotamers of trans- 1,2-cyclohexanedicarboxylateare calculated by this analysis (gauche form 60% and trans form 40%).
Introduction dianions, e g , malate9.10 and aspartate,' have been already determined from the N M R coupling constants. This method Several interesting studies have been reported on the steis applicable to the species showing ABX patterns of ' H N M R reoselectivity in outer-sphere association of metal complexes. spectra. However, it seems that this method is limited to the One of the familiar examples of this kind is on the stereosemonosubstituted succinate dianion. As for the disubstituted lective association of ~ - ( 2 R , 3 R ) - t a r t r a t e with A- and A-[C0(en)3]~+(en: ethylenediamine) in aqueous s ~ l u t i o n . ~ - ~succinate dianion, the information on the rotational isomerism is obtained from the comparison with the acid dissociation For the purpose of clarifying the origin of this stereoselectivity, constants.13 The result from this method is qualitative but we have investigated the ion-pair structure in solution between applied to the rotational isomerism between meso and dl acids the dicarboxylate anion and the complex ion. We have already of disubstituted succinate dianions. On the basis of the inforelucidated by measuring CD changes that the dicarboxylate mation on the rotational isomerism obtained in these manners, anion interacts with the complex ion through the carboxyl we attempted to make clear the contribution of the rotamers group (COO-), and that the skeleton I is essential to a favorto the interaction of monosubstituted and 1,2-disubstituted succinate dianions with the complex ion. F-c, \
I
-0oc
coo-
I
able association in this However, most of the dicarboxylate anions d o not exist as only one species in solution but as some rotamers. Therefore, the interaction of the dicarboxylate anion with the complex ion cannot be elucidated until the contribution of each rotamer to the interaction becomes clear. It is, a t present, not clear in detail how the rotamers contribute to the interaction with the complex ion. Thus we investigated the interaction of the rotamers of monosubstituted and 1,2-disubstituted succinate dianions with the complex ion by utilizing the CD measurement. I n solution, the rotational isomerism of dicarboxylate dianions can be investigated by means of the N M R technique. In fact, the fractional populations of rotamers of dicarboxylate 0002-7863/79/1501-4221$01.00/0
Experimental Section Materials. Tris(ethylenediamine)cobalt(lII)Bromide. [Co(en)3]Br3-3H30 was prepared and resolved into enantiomers, A- and A-[Co(en)3]Br3.H20, by using silver L-( +)-tartrate. The purity of these complexes was checked by elemental analysis and spectroscopic methods. Monochlorosuccinic and Monobromosuccinic Acids.I4 The preparation of these compounds was made by passing a stream of N z 0 3 mixed with N2 into ice-cooled aqueous solutions of (t)-aspartic acid and hydrochloric or hydrobromic acid. Monochlorosuccinic acid: [a]D -55' (ethyl acetate). Anal. Calcd for C4H504CI: C, 3 I .48; H , 3.30. Found: C, 31.27; H, 3.30. Monobromosuccinic acid: [ a ]-75' ~ (ethyl acetate). Anal. Calcd for C4H504Br: C, 24.39; H, 2.56. Found: C, 24.38; H , 2.57. dl-Dibromosuccinic Acid.Is This compound was prepared by the
0 1979 American Chemical Society
