3874 (13)R. F. Heck, J. Am. Chem. SOC.,85, 655 (1963). (14)M. Basato and A. Poe, J. Chem. SOC.,Dalton Trans., 456 (1974). (15) R. E. Davis, T. A. W s , T.-H. Hseu, J. C. Wagnon. T. Devon, J. Tancrede. J. S. McKennis. and R. Pettit, J. Am. Chem. SOC.,96,7562 (1974). (16)The experimental fact that the relevant reaction steps proceed only photochemically in the case of DMB but thermally with DPA may be rationalized by applying qualitative FMO theory." The coordinated alkyne in (L)Fe(C0)3(DPA)still has one of the degenerate HOMO'Savailable for intramolecular cycloaddition, while the diene in (L)Fe(C0)3(1.2-~-DMB) uses its \Ir, orbital for complexation and therefore cannot undergo the cycloaddition reaction by a thermal pathway.
(17) K. Fukui, Top. CurrentChem., 15, l(1970). (18) H. Kisch, J. Organomet. Chem., 30, C 25 (1971). (19)0.Diels and K. Alder, Justus Liebigs Ann. Chem., 490, 236 (1931);H. D. Scharf and D. Korte, Chem. Ber., 99,3925 (1966). (20) We are indebted to Professor E. Koerner von Gustorf for the loan of this anoaratus. -rr(21)J. G. Caivert and J. N. Pitts, Jr., "Photochemistry",Wiley, New York, N.Y., 1966,p 783:C. G. Hatchard and C. A. Parker, Proc. R. SOC.London, Ser. A, 235. 518 11956). (22)H. Hermann,'G.Koltzenburg. and D. Schulte-Frohlinde, Ber. Bunsenges. Phys. Chem., 77, 677 (1973).
Carbon-Hydrogen Bond Activation by Transition Metal Complexes. Oxidative Addition of Alkyl Methacrylate to Ruthenium. The Structure of Hydrido( 2-n-butoxycarbonylpropen yl-C l, U)tris(triphenylphosphine)ruthenium(11) Sanshiro Komiya,la Takashi Ito,la Martin Cowie,lb Akio Yamamoto,*la and James A. Ibers*lb Contribution from the Research Laboratory of Resources Utilization, Tokyo Institute of Technology, 0-okayama, Megura-ku, Tokyo 152, Japan, and the Department of Chemistry, Northwestern University, Evanston. Illinois 60201. Received November 17, I975
Abstract: Alkyl methacrylate reacts with dihydridotetrakis(triphenylphosphine)ruthenium(II) via vinylic C-H bond cleavage to give hydrido(2-alkoxycarbonylpropenyl-C1,~)tris(triphenylphosphine)ruthenium(II), RuH(CH=C(CH3)C(O)OR)(PPh3)3, accompanied by formation of an equimolar amount of alkyl isobutyrate per mole of the dihydrido complex. A hydridoalktnyl-type structure for the complex was proposed on the basis of chemical reactions, such as the formation of methyl cisP-deuteriomethacrylate on treatment of the complex with DCI, and methylation at the P-position of alkyl methacrylate on treatment with methyl iodide. The low u(C=O) band (-1580 cm-') in its ir spectrum, the presence of a hydride signal in the IH N M R spectrum, and the 3'P(1HIN M R spectrum characteristic of meridional octahedral configuration support the proposed structure. An x-ray study confirmed the structure of hydrido(2-n-butoxycarbonylpropenyl-C1,~)tris(triphenylphosphine)ruthenium(II). This compound crystallizes from tetrahydrofuran-diethyl ether in the space group Clh6-C2/c with a = 29.691 (8) A, b = 21.865 (5) A, c = 21.245 (6) A, = 122.26 (I)O, and Z = 8. Based on 4801 unique reflections with FO2 2 3a(FO2)full-matrix, least-squares refinement led to agreement indices (on F ) of R = 0.067 and R, = 0.1 11. The structure consists of discrete molecules of the complex in which the ruthenium atom is six-coordinate with distorted octahedral geometry. Three coordination sites are occupied by the phosphine ligands in a meridional arrangement. The alkyl methacrylate ligand is bidentate, bonded to the ruthenium atom via the vinylic carbon and the carboxyl oxygen atoms forming a R'U-C-Cfive-membered ring. The vinyl carbon atom is trans to a phosphine ligand and the oxygen atom is trans to the hydrido ligand. The terminal three carbon atoms of the n-butyl group of the n-butyl methacrylate ligand are disordered making a satisfactory description of their positions difficult. Some relevant metric parameters in the complex are: Ru-C( l ) , 2.061 (10) A; Ru-O(l), 2.246 (7) A; C(l)-C(2), 1.368 (15) A; C(2)-C(4), 1.442 (15) A; C(4)-0(1), 1.254 (12) A; O(1)-Ru-C(1), 75.6 (4)O; Ru-C(1)-C(2), 117.8 (8)O; C(l)-C(2)-C(4), 113.4 (l0)O; C(2)-C(4)-0(1), 121.2 (11)O; and C(4)-O(l)-Ru, 1 1 1.6 (7)O.
Activation of a C-H bond by a transition metal complex is attracting increasing interest because of its potential utility in synthetic organic chemistry. Oxidative additions involving C-H bond cleavage have been postulated in ethylene dimeriati ion,^,^ oxidative substitution of an olefin assisted by palladium compound^^-^ and in H-D exchange in aliphatic and/or aromatic hydrocarbons catalyzed by tantalum, niobium, iridium,*v9 platinum,1°-13 titanium,I4,l5 rhodium,I6 cobalt,I7 and rhenium compounds.18 However, unequivocal examples of isolation of the product of oxidative addition involving C-H bond cleavage are relatively limited, except for a few examples of orthometalation and its analogous reactions in which C-H bond cleavage of a coordinated ligand is i n v ~ l v e d . lMeta~-~~ lation of a vinylic carbon atom to form metal-sp*-carbon a-bonds has been reported for platinum,33 rhodium,34 and Journal of the American Chemical Society
/
98:13
iridium,35all of which involve nitrogen as a donor atom. In the course of our systematic studies on the reaction of dihydridotetrakis(tripheny1phosphine)ruthenium (1) with various substituted olefins, we found that alkyl methacrylate reacts with 1 via vinylic C-H bond activation to yield hydrido-2alkoxycarbonylpropenyl-typecomplexes. The present paper reports in detail the preparation and characterization of these novel compounds with a series of ester-alkyl groups, and the crystallographic determination of the structure of one of these complexes, hydrido( 2-n- butoxycarbonylpropenyl-CI, 0 )tris(triphenylphosphine)ruthenium(II). A preliminary account has been published elsewhere.36 Isolation of the hydrido carbon-to-metal a-complexes by the direct oxidative addition involving C-H bond cleavage has also been reported for naphthalene,19-21b e n . ~ e n e , ~ 'p-xylene . ~ ~ - ~ ~and m e ~ i t y l e n e , ~ ~
/ June 23, I976
3815 Table I. Analyses and Physical Roperties of RuH(CH=C(CH,)C(O)OR)(PPh,), Complex R
Amearance
(2)
Analyses0 C% H%
Mpb CC)
YieldC (%)
~~
Me (2a)
Light yellow powder Et (2b) Yellow prisms i-Pr (2c) Yellow needles n-Bu (2d) Yellow prisms
70.0d (71.7) 5.4 (5.4) 211-213
73
72.3 (72.0)
5.4 (5.7) 200
83
72.4 (72.1)
6.3 (5.6)
178-180
25
72.8 (72.3)
6.2 (5.7)
165-167
15
UCalculated values are in parentheses. bWith decomposition. CYields are calculated on the basis of the starting dihydrido complex 1. dGood analytical value is not obtainable owing to difficulty in purification of the product (see text). Table 11. Infrared Data for Hydrido-o-Alkenyl Complexes (cm-')a Complex Rb
~(Ru-H)
v(C=O)
Me (2a) Et (2b) i-Pr (2c) n-Bu (2d)
1980 m 1'980 m 1960 m 1960 m
1590 s 1580 s 1580 s 1580 s
a K B r disk. Intensity abbreviations: s, strong; m, medium. bDesignation of R is as indicated in Table I.
and other 0 1 e f i n s . ~ However, ~-~~ this paper presents, we believe, the first crystallographic evidence for oxidative addition involving vinylic C-H bond cleavage.
Experimental Section All manipulations were carried out under nitrogen or under a vacuum. Solvents were dried in the usual manner, distilled, and stored under nitrogen. Analysis of evolved gas was carried out by mass spectrometry and gas chromatography after collecting gases fractionally using a Toepler pump, by which the volumes of gases were also measured. Analyses of liquid products were carried out by GC-mass spectroscopy (JEOL JNS- 100 GC-mass spectrometer) and gas chromatography (Shimadzu Model GC-3BT). Infrared spectra were recorded on an Hitachi EPLG3 spectrometer using KBr pellets prepared under an inert atmosphere, Measurement of N M R spectra obtained on a JEOL PS-100 spectrometer was carried out by Mr, Y Nakamura.la 'HN M R signals are referred to tetramethylsilane and 31P11HJN M R signals to triphenylphosphine (downfield positive). Microanalyses were carried out by Mr. T. SaitoIP using a Yanagimoto C H N Autocorder Type MT-2. Dihydridotetrakis(triphenylphosphine)ruthenium(II), RuH2( P P ~ J )1,~and , ~its~ deuterido analogue, R u D z ( P P h ~ - d & ~ ~were q~* prepared by the methods reported previously. Commercially available methyl, ethyl, isopropyl, and n-butyl methacrylates and methyl iodide were used after distillation over CaH2 in vacuo, Ethyl cis-b-deuteriomethacrylate was synthesized from methylacetylene, nickel carI
bonyl, and ethanol-d,, according to the method described in the literat~re.~~ Reaction of 1 with Methyl Methacrylate,, Excess methyl methacrylate (15.0 ml) was introduced to complex 1 (1.185 g, 1.03 mmol) by trap-to-trap distillation. After a day at room temperature, a light yellow precipitate (2a) was formed, which was filtered off, washed with n-hexane, and dried under vacuum. Because of the difficulty in separating the resulting complex from the polymer formed, a reliable analytical value could not be obtained (Table I). Pouring the yellow solution into acidic methanol caused precipitation of poly(methy1 methacrylate), which was identified after filtration, washing with methanol, and drying under vacuum (yield, 0.1 1%). Thermolysis of complex 2a (413 mg, 0.418 mmol) at ZOOo liberated 0.345 mmol of methyl methacrylate (83%). Reaction of 1 with Ethyl Methacrylate. Ethyl methacrylate (3.0 ml) was added to complex 1 (861 mg, 0.748 mmol) by trap-to-trap distillation. After a day at room temperature a yellow precipitate was separated from the homogeneous yellow solution and the formation of ethyl isobutyrate (0.53 mmol, 70%) in the solution was confirmed. The precipitate was crystallized from a mixture of tetrahydrofuran (THF) and diethyl ether as yellow prisms of 2b which were washed several times with n-hexane and dried under vacuum. The yield and analytical data are shown in Table I. Thermolysis of complex 2b (5 12 mg, 0.519 mmol) at 200° liberated 0.40 mmol of ethyl methacrylate and 0.055 mmol of ethyl isobutyrate. Total yield of the esters liberated on thermolysis was calculated as 88% on the basis of 2b. The reaction of ethyl cis-P-deuteriomethacrylate with 1 was similarly carried out. Partial deuteration of the hydridic hydrogen atom in the reaction product was demonstrated by a decrease of relative intensity of u(Ru-H) in its ir spectrum compared with the undeuterated analogue (Table 11). Reaction of 1 with Isopropyl Methacrylate. Isopropyl methacrylate (5.0 ml) was added to complex 1 (978 mg, 0.850 mmol) to give a homogeneous solution in a day at room temperature. In the solution isopropyl isobutyrate (0.878 mmol, 103%) was detected. A yellow precipitate was obtained by addition of n-hexane to the solution. This precipitate was crystallized as yellow needles of 2c from THF-diethyl ether, washed with n-hexane, and dried under vacuum. Reaction of 1 with RButyl Methacrylate. n-Butyl methacrylate (5.0 ml) was added to complex 1 (1600 mg, 1.39 mmol) to give a yellow precipitate in a day at room temperature. In the solution n-butyl isobutyrate (1.59 mmol, 1 1 4%) was detected. The precipitate was crystallized as yellow parallelepipeds of 2d from n-hexane and dried under vacuum. Reaction of RuD2(PPha-d& with Ethyl Methacrylate. Excess ethyl methacrylate reacted with RuDz(PPh3-d6)4 to give R'uH(CH-
= C ( C H J ) C ( ~ ) ~ C ~ H ~ ) ( P P ~ , .3,~ ,The ) , , ir spectrum of the resulting hydrido-a-alkenyl complex showed no decrease in the relative intensity of the v(Ru-H) band and little change was observed in the ir band attributable to ortho-deuterated triphenylphosphine ligands. Thermal decomposition of the resulting complex at 200° gave deuterated ethyl methacrylate. Methyl and vinyl protons were deuterated as revealed by N M R spectroscopy (Table 111). The extent of deuteration is listed in Table IV. Reaction of 2a and 2b with Hydrogen. Under a hydrogen atmosphere heterogeneous benzene solutions of complexes 2a and 2b became homogeneous in a few hours at room temperature and after a
Table 111. 'H and "P ('HI NMR Data for Hydrido-o-Alkenyl Complexesa Complex, Rk 'H NMR
Ru-H
=ccg,
=CH R "P NMR
Pa ph
-18.2 (t.d.)d 1.94 (s)
-e
-CHIC!, 1.32 (t)g -CHlCH3 3.98 (q)8 -56.4 (d)f 51.3 (t)'
-18.0 (t.d.)d 1.32 (s) 8.16 (qLf -CH(CH,), 1.28 (d)h -CH(CH,), 4.76 (sep)h 51.6 (d)j 48.4 (t)i
-17.9 (t.d.)d 1.30 (s) 8.16 (q)f 1-2 (m) 3.68 (m) 51.8 (d)i 48.3 (t)i
a 100 MHz and 40.5 MHz for 'H and "P NMR, respectively. Values in parts per million referred to Me,Si and PPh,, downfield positive, for 'H and "P NMR spectra, respectively. 'H NMR signals from PPh, which occur at 7.5-8.5 ppm are omitted. Multiplicity abbreviations: t.d., triplet of doublets; d, doublet; s, singlet; t , triplet; q, quartet; sep, septet; m, multiplet. b In CH,CI,. C I n toluene-d,. d IIJ(P,-H) I = 28 Hz; I'J(Pb-H) I = 12 Hz. eThe signal was not observable owing to the oor solubility of the complex. f14J(H-H) I = 4 Hz. g 1 'J(H-H) I = 7 Hz. I?I(H-H) I= 6 Hz. I'J(P,-Pb) I = 24 Hz. I'J(P,-Pb) 1 = 23 Hz. Designation of R is as indicated in Table I.
R
Yamamoto, Ibers, et al.
/
Addition of Alkyl Methacrylate to Ruthenium
3876 Table IV. Extent of Deuteration in Ethyl Methacrylate Released by Pyrolysis of Complex 3
Table V. Summary of Crystal Data and Intensity Collection Compound Formula weight Formula a
b
Protonsa No. of protons expecJedb No. of protons foundc Degree of deuteration, 70
C
a
b
C
d
e
3 1.13 62
1 0.34 66
1 0.28 72
2 1.86 7
3 3.00 0
UDesignation of each proton is as shown in structure above. bNumber of protons expected when no deuteration is present. CNumber of protons calculated from the 'H NMR spectrum of the recovered ethyl methacrylate by assuming that the proton e is not deuterated. day white needles deposited. In the solutions hydrogenated products of these olefins were detected. The white needles were recrystallized from benzene and n-hexane mixed solvent. Anal. Calcd for C54H49P3R~:C, 72.7; H , S.5. Found: C, 72.2; H , 6.2. An ir spectrum of these needles showed a v(Ru-H) band47-50a t 1940 cm-l. By treating the needles with excess ,triphenylphosphine in benzene, RuH2(PPh3)4 was formed with evolution of hydrogen a t room temperature. Reaction of 2b with dry HCI. Excess, dry hydrogen chloride (50 ml, STP) was introduced to complex 2b (540 mg, 0.54 mmol) in diethyl ether by trap-to-trap distillation under vacuum. The color of the solution changed to orange and ethyl methacrylate (0.56 mmol, 103%) was detected in solution by gas chromatography. Hydrogen (1 1.2 ml, 0.50 mmol, 93%) was evolved as determined by mass spectroscopy. Reaction of 2a with DCI. Excess, dry deuterium chloride (isotopic purity 95%) reacted with 2a in benzene-d6 to give methyl cis-P-deuteriomethacrylate; isotopic purity was calculated as 46% by comparing the peak area of the N M R spectrum of the recovered methyl cis-@deuteriomethacrylate. Gaseous D2, H D , and H2 in a ratio of 60:34:6 were also evolved. Reaction of 2a with Methyl Iodide. Excess methyl iodide (3.0 ml) reacted with 2a (558 mg, 0.585 mmol) to give a brown heterogeneous solution in a day at room temperature. In the solution methyl angelate (0.007 mmol), methyl tiglate (0.08 1 mmol), methyl methacrylate (0.341 mmol), and small amounts of hydrogenated products of these olefins were detected by GLC-mass spectroscopy. Methane (0.554 mmol) was detected in the gas phase. Reaction of 2b with Methyl Iodide. In a day at room temperature, excess methyl iodide (3.0 ml) reacted with 2b (705 mg, 0.704 mmol) similarly to give methane (0.641 mmol), ethyl angelate (0.083 mmol), ethyl tiglate (0.188 mmol), ethyl methacrylate (0.265 mmol), and small amounts of their hydrogenated products. Reaction of 3 with Methyl Iodide. Complex 3 (220 mg, 0.230 mmol) was allowed to react with 3 ml of methyl iodide in an analogous way as above. In this reaction, methane (0.233 mmol, 101% on the basis of the complex 3) was evolved in which ca. 10% of CH3D was detected by means of mass spectroscopy. In solution ethyl methacrylate (31%) and ethyl tiglate (36%) were detected by gas chromatography. X-Ray Data Collection. Yellow prisms of t h e complex, RuH(CHC(CH~)CO~C~H~)(PP~~)~, suitable for x-ray diffraction studies were obtained from a THF-diethyl ether solution. The crystalline compound is stable in air for only a few hours but seems to be stable when stored under N2. Therefore immediately upon removal from solution, crystals were mounted in N2-filled capillaries. Preliminary film data showed that the crystals belong to the monoclinic system, having extinctions (hkl, h k = 2n 1; hOl, 1 = 2n + 1) characteristic of the space groups Cs4-Ccand C2h6-C2/c. The centrosymmetric space group was chosen and later verified by: ( I ) the successful refinement of the structure with acceptable positional parameters, thermal parameters, and agreement indices; (2) the location of all 45 phenyl hydrogen atoms in difference Fourier syntheses: (3) the statistical equivalence of 177 pairs of symmetryrelated reflections. Accurate cell parameters were obtained by a least-squares procedure based on the angular setting for 18 handcentered reflections from diverse regions of reciprocal space (54.3'' I20 I33.3'), using a narrow x-ray source. See Table V for pertinent crystal information and details of data collection. The mosaicity of
+
+
Journal of the American Chemical Society
/
98:13
/
P V 2
Den sit y Space group Crystal dimensions Crystal shape Crystal volume Temperature Radiation Transmission factors cc Receiving aperture Takeoff angle Scan speed Scan range Background counts 20 limits Final no. of variables Unique data used F,' 2 3u (Fo2) Error in observation of unit weight
RuH(CHC(CH,)CO,C,H,)(P(C,H,),), 1030.15 amu C,2H,,O,P,Ru 29.691 (8) A 21.865 (5) A 21.245 (6) A 122.26 (I)" 11662.8 A' 8 1.173 g/cm3 (calcd) 1.19 (1) g/cm3 (exptl) c2h6-C2/c 0.40 X 0.56 X 0.18 mm Monoclinic prisms 0.0416 mm3 22 "C Cu Kcu, ( h 1.540562 A) 0.316-0.567 32.99 cm-' 6.0 x 6.0 mm; 30 cm from crystal 3.8" 2.0" in 20/min 1.1" below K a , to 1.1" above K a 2 for 20 81.0"; 1.2" and 1.2" for 20 > 81.0" 10 s for 20 < 70.0", 20,s for 20 i 86.0", 40 s for 20 > 86.0" 3.0 - 100.On 224 4801
4u(FO2)and 10 had lFo2 - Fc2J> 5u(FO2).There were no trends of the quantity x:w(lFd - I F d ) 2as a function oflFd or Miller indices. However, agreement was poorer a t lower values of 8, as expected in view of the disorder of the n-butyl group. The final positional and thermal parameters of atoms and groups appear in Tables VI, VII, and VIII. Root-mean-square amplitudes of vibration are given in Table IX.54A listing of the observed and calculated structure amplitudes for the data used in the refinements is available.54
RuH,(PPh,),
Results and Discussion Preparation of Hydridopropenyl Complexes. W e have reported previously that dihydridotetrakis(tripheny1phosphine)ruthenium(II) (1) reacts with olefins such as ethylene and styrene to afford olefin-coordinated complexes, Ru(olefin)(PPh3)3, together with formation of the hydrogenated products of the olefins.55 When a large excess of ethyl methacrylate was allowed to react with 1 a t room temperature, a
RuH,(PPh,), 1
-
+ CH,=C(CHJCOOR
1 --t
RuH(CH=C(CH,)C(O)OR)(PPh,), 2
+ (CH3)zCHCOOR + PPh; R
=
(1)
Me(&), Et(Pbj, i-Pr(2c), and n-Bu(2.d)
yellow complex with an apparent composition of Ru(ethy1 methacrylate)(PPh3)3, precipitated out in a day with the concomitant formation of 1 mol equiv of ethyl isobutyrate, the hydrogenation product of ethyl methacrylate. Analyses of the complex by means of infrared and N M R spectra, elemental analyses, and chemical reactions, however, all suggest that this diamagnetic complex is hydrido(2-ethoxycarbonylpropenylC',O)tris(triphenylphosphine)ruthenium(II) (2). This formulation is confirmed by an x-ray diffraction study of the nbutoxy complex (vide infra). Isopropyl and n-butyl methacrylates react similarly with complex 1 t o yield the corresponding hydrido-a-propenyl complexes (2c and 2d, respectively). The reaction of 1 with methyl methacrylate accompanied the polymerization reaction56 and the reaction products are always contaminated with a small amount of poly(methy1 methacrylate); hence the purification of complex 2a and detection of the hydrogenated product were difficult. Results of elemental analyses and physical data of complexes 2a-d are listed in Table I. Reaction of ethyl cis-P-deuteriomethacrylate (isotopic purity 72%) with complex 1 gave 2, in which the hydridic hydrogen atom was only partially deuterated.
--+
+
H
,CK
'C=C
D'
(excess)
'COOEt
RuH*(CH*=C(CH,*)C(O)OEtj(PPh,),
+ PPh,
An asterisk implies partial deuteration.
Yamamoto, Ibers, et al. / Addition of Alkyl Methacrylate to Ruthenium
3878 Table VII. Derived Parameters for the Rigid Group Atoms of RuH(CHC(CH~)COOC~H~)(PP~~)~
?!%
.....4.4~.....*........ .....L......... .... 2
*?it*.+
!*.~.***~*
X?!L.*.*..*L.*
......?:?t.*
........*r..........*...f.,..*
C l l l l
0.238081271
0.0148 131
0.2110131
3.46(201
c1541
0.4253 1 3 1
O.O3ZZ( 41
0.450415l
7.7141
c1121
0.237191281
0.05131(241
0.1567 141
4.171231
C155l
0.4223131
0.0881141
0,4792 (31
7.2131
c1131
0.259113l
0.0298 131
0.1170 141
5.151261
Cl561
0.5555131
0.131813l
0.4324141
5.531271
c1141
0.2818 131
-0.0281131
0.1316141
5.50 1271
C1611
0.312413l
0.1807(41
0.2198141
4.20 I 2 2 1
GI151
0.2827 131
-0.06466126l
0.1859(41
5.93 I 2 9 1
Cl62l
0.27057125l
0.2001141
0 a 1505l i l
5.311261
Cllbl
0.2608131
-0.04319(281
0.2256 ( 4 1
4.75 1241
C(631
0.278713)
0.2088(41
0.0924(31
7.1(31
GI211
0.24126 I 2 5 1
0.000431291
0 . 3 4 6 9 ( 31
3.591201
C(64l
8.3287141
0.1981(41
0.1036141
7.2131
c1221
0.28312128)
0.02730 I 2 4 1
0.410914l
4.341231
Cl651
0.37050 1291
0.1787 151
0.172815l
8.5141
CI23l
0~311121261
-0.006413l
0.4765 131
5 . 8 1 1281
C1661
0.36236(271
0.170014l
0.2309141
6.6131
c1241
0.2972 131
-0.0669131
0.4781131
6.2131
C(711
0.15109127l
0.23979127)
0.34531kI
3.72(211
c1251
0.2554131
-0.093751241
0.4140 1 4 1
5.8212Rl
c1721
0.200091231
0.26911 31
0.3fl70141
4 . 2 3 1 221
Cl26l
0.22738(251
- 0 . 0 6 0 1 (31
0 . 3 4 8 4 (31
4.501231
C(731
0.20665(231
0.3166131
0.4 34 8 141
5.11125)
GI311
0.14135(201
0.0162131
0.207013l
3.54(201
Cl74l
D.1~42131
0.3348 1 3 1
0.440 9 ( 4 1
5.731281
c 1321
0.11651 I 2 5 1
0.0151(31
0.1299131
4.24(271
GI751
0.11520 I 2 6 1
0.3055(41
0.5991151
6,1131
C133I
0.065021261
-0.007913l
0.085781251
4.90 1251
Cl76l
o.in8~41zi1
0.2580 131
0.3513141
5.171261
c 1341
0.03837(201
-0.0297141
0.1187141
5.62 ( 2 7 1
CI811
0~127061261
0.117891281
0 . 3 3 3 3 131
3.641201
CIS51
0.06321(261
-0,0287 (31
o.i95n((ri
5.19 ( 2 6 )
CI82l
0 17025 (191
0.0906131
0.3'355 ( 4 )
3.98(221
C1361
0.11469 1 2 5 1
-0.0057 131
0.239931251
3.931211
Cl83l
0.?61781251
0,0487 1 3 1
0.437413)
5.19 I 2 6 1
Clbll
0.32442128l
0,246951241
0.3(132(31
3.471201
C(841
0.1101131
0.0341(31
0 * 4172 I 4 1
5.69127)
GI421
0.323281281
0.25760127l
0.406914l
3.8412ll
GI851
0.06693(211
0.0613131
0.3550141
5.401261
Cl43l
0.340313l
0.31361 31
0.4435131
4.69(241
GI861
0.07540 ( 2 2 1
O.lO32131
0.313013l
4.65 1241
CI441
0.3585131
0.35887(251
0.416414)
5,681281
C(91l
0.078321241
0.1922131
0.1992(31
3,781211
c1451
0.359613)
0.348251281
0.3527141
5.90 1 2 f l I
c1921
0.0384131
0.144691241
0.150414l
4.661241
Cl461
0~3426131
0.2923131
0.3161(31
4.~81251
c1931
0.00283 1291
0.15751 31
0.0816(41
6.3131
C151l
0~351641271
0.1196131
0.3569141
3.82121l
c1941
-0.OlZR3(271
0.2179 141
0.0604(31
6.4131
c 1521
0 , 3 5 4 6 131
0.0637 141
0.3281(31
5.57 127 I
C195l
0.01711 31
0.265921261
0.1082(41
6.3131
C(531
0.3915 141
0 6 0 1997 1291
0.374q151
7.313)
Cl'36l
0.06271 11
0.25257 1 2 7 1
0.177114)
5.051261
In this reaction the ethyl cis-0-deuteriomethacrylate used in excess was converted into ethyl methacrylate which contained ca, 14% of deuterium a t vinylic positions and the amethyl group as revealed by the IH N M R spectrum of the recovered methacrylate. Thus scrambling of the propenyl protons of the ethyl methacrylate took place in the reaction (vide infra). The triphenylphosphine ligand was not deuterated in this reaction. R ~ J & ( P P h 3 - d 6 ) 4 , ~in ~ *which ~ * 87% of the hydridic hydrogen atoms and ortho-hydrogen atoms of the triphenylphosphine ligand were deuterated, reacted with ethyl methacrylate similarly to give the hydrido-g-alkenyl complex, R ' u K
(CH=C(CH&(b)OEt)(PPhpd6), 3, in which the hydridic hydrogen atom was not deuterated. Complex 2 was also obtained by reaction of the ethylene complex, R u ( C ~ H ~ ) ( P Pwith ~ ~ ethyl ) ~ , methacrylate ~~ with no production of ethyl isobutyrate. Therefore, the reaction of 1 with alkyl methacrylate may actually involve the oxidative addition of alkyl methacrylate to a zero-valent ruthenium complei which has been produced by insertion of the alkyl methacrylate into a Ru-H bond, followed by reductive elimination of the hydrido-alkyl type complex. The most straightJournal of the American Chemical Society
/
98:13
forward explanation for the oxidative addition of alkyl methacrylate to the Ru(0) complex is the splitting of the C-H bond a t the vinylic group. Another less straightforward pathway involves C-H bond splitting a t the a-methyl group of the methacrylate forming a n-allyl-hydrido type complex which then rearranges to the 2-alkoxycarbonylpropenylcomplex by hydrogen transfer. We favor the mechanism involving the splitting of the C-H bond a t the vinylic group since a similar reaction has been observed in the reaction of a methyl-copper complex with vinyl acetate which has no a-methyl groups5' However, the H-D scrambling reaction involving the a-methyl group of the alkyl methacrylate suggests that the n-allylic intermediate may intervene in the scrambling process (vide infra). Infrared Spectra. Ru-H and carboxyl stretching frequencies of complex 2 are summarized in Table 11. The complete disappearance of the band at 2080 cm-I assigned to v(Ru-H) of the starting dihydrido complex 146347 and the appearance of a new u(Ru-H) band a t 1960-1980 cm-l suggest formation of a new type of hydrido complex. In the ir spectrum of 3, which was prepared from RuDz(PPh3-d6), no v(Ru-D) band was observed and the u(Ru-H) band was observed a t the same frequency as that of 2b. The out-of-plane phenyl C-H and C-D
1 June 23, 1976
3879 deformation bands in the ir spectrum of 3 were essentially the same as those in the spectrum of RuD2(PPh3-d6)4. These results clearly indicate that the hydridic hydrogen atom in 2 or 3 comes neither from the original hydridic hydrogen atoms in 1 nor from ortho-hydrogen atoms in the triphenylphosphine ligands, but most probably from the hydrogen atom adjacent to the double bond in the methacrylate. The ester carboxyl stretching frequency which occurs a t 1720-1730 cm-l in the starting alkyl methacrylate exhibits a 140 cm-' shift to lower frequency on complex formation. This may be explained if there is ring formation involving the coordination of the C=O moiety through the oxygen atom to the ruthenium at6m. In such a ring the carboxyl double bond order will decrease. A shift of u(C=O) towards lower frequency has been reported for the complex formed between methyl methacrylate and zinc chloride.58 More recently, van Baar et al. reported that the u(N=N) vibration in IkHCI(C6H4N=IbPh)(PPh3)2, where coordination of nitrogen to form a chelate ring is also c o n ~ i d e r e d is, ~much ~ lower than that of the free ligand vibration. NMR Spectra. Owing to the poor solubility of complex 2a, N M R studies were carried out on complexes 2b, 2c, and 2d. As is shown in Table 111, proton-decoupled 31PN M R spectra of the complexes indicate the presence of two kinds of the triphenylphosphine ligands, Pa and P b . The doublet a t the lower
H 2
field is assignable to two triphenylphosphine ligands in the mutually trans positions (Pa) and a triplet a t a higher field to the triphenylphosphine trans to the vinylic entity (Pb). ' H N M R spectra show the resonance of a hydridic hydrogen nucleus at ca. -18 ppm as a triplet of doublets indicating the different coupling constants between J(H-PI) (28 Hz) and J(H-Pb) (1 2 Hz). The signal of the vinylic proton appears a t a very low field (8.2 ppm) with a coupling to three phosphorus atoms. Disagreement of this low 6 value with the reported value of 4.86 ppm for the corresponding vinylic proton in chloro(2methyl-3-(dimethylamino)propenyl)(triphenylphosphine)p l a t i n ~ m ( I 1 )and ~ ~ of 1.58 ppm in the metalated 2-(methy1azo)propene complex of iridium35 suggests that the chemical shift of the proton on a carbon atom attached directly to the metal is very sensitive to the electronic environment of the metal. The 'H N M R spectra of complex 2d observed in the presence of an equimolar amount of n-butyl methacrylate in C6D5CD3 at room temperature and at 90 OC can be accounted for as a simple mixture of each component, indicating that no exchange between the vinylic entity and the free methacrylate takes place in this system. The ' H N M R spectrum of 2c in pyridine shows some broadening of the a-methyl proton signal a t 100 OC. This may be related to formation of the hydrido7-allylic intermediate (vide infra). An attempt to observe the coalescence of the methyl resonance with the vinyl resonance failed owing to decomposition of the complex at higher temperatures. Thermolysis. Pyrolysis of complexes 2 in the solid state at 200 OC liberates over 0.8 equiv of methacrylic esters together with small amounts of their hydrogenation products and
benzene, which must arise from decomposition of the triphenylphosphine ligands. Thermolysjs of 3, the ortho-deuterated analogue of 2, at 200 OC liberates ethyl methacrylate in which ca. 70% of the vinylic and a-methyl protons are deuterated (Table IV) as analyzed by its 'H N M R spectrum. Thus there is exchange of the vinylic and a-methyl protons of ethyl methacrylate with the ortho-deuterium atoms of the triphenylphosphine ligands. The extent of this exchange was calculated to be 68%. The scrambling, including the a-methyl protons, suggests that a hydrido-7-allylic species such as CH,,
\A -
Ru-ICCOOR
is involved in the thermolysis with participation of ortho metalation of the triphenylphosphine ligands. Scrambling of the vinylic and a-methyl protons, but without participation of the ortho-phenyl protons, was also observed in the reaction of cis-0-deuteriomethacrylate with 1 (vide supra). A similar hydrido-n-allylic intermediate may also be involved in the reaction. The presence of a similar equilibrium between a propylene complex and a hydridoallyl complex has been reported by B~nneman.~~ Reaction of.2 with H2. Complex 2 reacted with hydrogen in benzene at room temperature to afford alkyl isobutyrate and the known tetrahydridotris(tripheny1phosphine)rutheni ~ m . ~ This ' , ~ feature ~ of the reaction is similar to those observed in the reactions of hydrogen with olefin coordinated complexes, R ~ ( o I e f i n ) ( P P h 3 ) 3 . ~ ~ Reaction of 2 with gaseous HCI and DCI. Complex 2b was allowed to react with excess HCI gas in diethyl ether a t room temperature releasing equimolar amounts of ethyl methacrylate and gaseous hydrogen. Dry DCI with an isotopic purity of 95% reacted with 2a in benzene46 at room temperature to afford 1 mol equiv of a 1:1 mixture of methyl methacrylate and methyl cis-/3-deuteriomethacrylate and 1 mol equiv of hydrogen gas containing H2, HD, and D2 in a ratio of 6:34:60. The result suggests that the vinylic entity in 2 is bonded to ruthenium at the cis position with respect to the ester group and that the reaction proceeds as shown in Scheme I. DCI probably adds oxidatively to 2 to give an unstable intermediate 4 containing both hydrido and deuterido ligands. Reductive elimination of 4 would then produce the cis-0-deuteriomethacrylate and the undeuterated methacrylate leaving a 2 : 1 mixture of RuHCI(PPh3)3 and RuDCI(PPh3)3, which on further reaction with DC1 would liberate the mixture of H2, HD, and D2. Calculated ratio of H2:HD:D2 from DCI of the 95% isotopic purity is 8:41:5 1 which is in approximate agreement with the experimental value. Reaction of 2 and 3 with Methyl Iodide. Complex 2b reacts with an excess amount of methyl iodide at room temperature to liberate 1 mol equiv of methane and a mixture of ethyl methacrylate (38% on the basis of complex 2b used), ethyl angelate 6 (12%), ethyl tiglate 7 (27%), and a small amount of ethyl isobutyrate as confirmed by GLC-mass spectroscopic analysis. Complex 2a reacts similarly with methyl iodide to yield analogous methyl esters (methyl methacrylate, 58%; methyl angelate, 1%; and methyl tiglate, 14%). On raising the reaction temperature the ratio of methyl tiglate to methyl angelate increases indicating that the isomerization of methyl angelate, initially produced by methylation, to methyl tiglate takes place in the course of the reaction. Methyl angelate has an inherent tendency to isomerize spontaneously to methyl tiglate at elevated temperatures. Possible pathways of this reaction are summarized in Scheme 11. Methyl iodide oxidatively adds to 2 to give an unstable hydridomethyl intermediate
Yamamoto, Ibers, et al.
Addition of Alkyl Methacrylate to Ruthenium
3880 Scheme I
H
I
(PPh, )&I
OR
/-c'
addition
H 2
4
+'
reductive elimination
Scheme I1 H (Ph,Pi3Ru\
I
/'%?'
H/C-C\CH3
OR
+CHJ
oxidative addition
'Clc
H'
,COOR C ' H,
Table X. Selected Distances (A) in RuH(CHC(CH,)CO,C,H,)@Ph,),
H
(PhJ'),Ru
Ru-P(l) I
H
/ H
\CH,
redudiw
6
I
CH,
isomerization
4
Ru-H(12) 0(1)-H(12) 0(1)-H(62) C(4)-H(62) C(ll)-H(52)
5 which on reductive elimination is converted into a mixture of hydridoiodo- and methyliodo-complexes liberating methyl angelate 6 and ethyl methacrylate. The hydridoiodo complex would react further with a mole of methyl iodide to release methane. Another portion of methane may be produced from a methyliodo intermediate via ortho-proton participation. In fact, ca. 10% e hof-HC evolved methane when complex 3, RuH(CH=C( CH3)C( 0 ) O E t ) (PPh3-d6)3, was allowed to react with methyl iodide at room temperature. The somewhat low CH3D content may be an indication that an H-D exchange involving the ortho metalation of 5 may intervene prior to the reductive elimination, but we did not examine the deuterium contents in the liberated esters. Description and Discussion of Structure. The complex, R u H ( C H C ( C H ~ ) C O ~ C ~ H ~ ) (consists P P ~ ~ ) of ~ , discrete monomeric units as is shown in the stereoscopic packing view in Figure 1. There are no unusual intermolecular contacts (see Table X). A three-dimensional representation of the molecule, showing the numbering scheme used, is presented in Figure 2. Figure 3 shows the inner coordination sphere including the entire n-butyl methacrylate ligand. Some relevant bond distances and angles are shown.
Journal o f t h e American Chemical Society
RU-H(~)~
/
98.13
Bond Distances 2.370 (3) C(6)-C(7) 2.327 (3) C(7)-C(8) 2.311 i3j P(l)-C(ll) 2.061 (10) P(l )-C(2 1) 2.246 (7) P(l)-C(3 1) 1.368 (15) P(2)-C(41) 1.535 (15) P(2)-C(51) 1.442 (15) P(2)-C(61) 1.254 (12) P(3)-C(71) 1.327 (13) P(3)-C(8 1) 1.454 (18) P(3)-C(91) 1.70 (4) Nonbonded 2.81 3.07 2.36 2.59 2.52 2.52
Distances C(26)-H(16) C(42)-H(56) C(42)-H(72) C(61)-H(46) H(42)-H(72) H(42)-H(56)
1.75 (7) 1.3 (21 1.856 (10) 1.838 (6) 1.864 (6) 1.858 (6) 1.842 (7) 1.841 (11) 1.852 (8) 1.838 (9) 1.851 (5) 1.849 (1l)a 2.52 2.43 2.56 2.50 2.19 2.28
aThe estimated standard deviation is the larger of an individual standard deviation or the stapdard deviation of a single observation as calculated from the mean. bH(1) is attached to C(1).
The ruthenium atom is six-coordinate, with a distorted octahedral environment. Three of the coordination sites are occupied by the phosphines in a meridional arrangement and two are occupied by the bidentate n-butyl methacrylate ligand, coordinated to ruthenium via the vinylic carbon atom and carboxyl oxygen atom. The hydrido ligand completes the coordination about ruthenium. Two phosphines are mutually trans while the third is trans to the vinylic carbon atom. The hydrido ligand is trans to the oxygen atom. The coordination geometry in this complex is remarkably similar to that in two closely related complexes, RuH(02CMe)(PPh3)3, an effective hydrogenation catalyst,6' and R u H ( O ~ C H ) ( P P ~ In ~ ) these ~ . ~ ~complexes the n-butyl methacrylate ligand is replaced by the bidentate acetate and formate ligands, respectively. The similarities in the geometries are especially evident in the metric parameters of the triphenylphosphine ligands. For the methacrylate, acetate, and formate complexes, respectively, the trans P-Ru-P angles are 152.5 (l)', 154.9 (l)', and 151.5 (6)'. ThecisP-Ru-Pangles
/ June 23, 1976
388 1
Figure 1. A stereo drawing of a unit cell of RuH(CHC(CH~)CO~C~H~)(PP~~)~. The x axis is horizontal to the left, they axis runs from top to bottom, and the z axis comes out of the paper towards the reader. Vibrational ellipsoids are drawn at the 20% level except for the terminal three atoms of the n-butyl group which are drawn arbitrarily small here and subsequently for clarity.
RIN
P
B
RING 3
RING I
Figure 2. A molecule of RuH(CHC(CH~)CO~C~H~)(PP~~)~ showing the numbering scheme used. Hydrogen atoms are omitted for clarity of the drawing. Vibrational ellipsoids are shown at the 20% level, except C(6). C(7), and C(8).
for these same complexes are: 99.62 (lo)', 99.30 (9)'; 98.6 (l)", 99.7 (2)O; and 98.2 (4)O, 101.4 (4)O. These angles reflect both the repulsive interactions between the bulky phosphine ligands with all cis P-Ru-P angles greater than the ideal 90°, and the reduced steric requirement of the hydrido ligand, with the phosphines bent towards this coordination site. Only P( 1) in the present complex does not seem to be bent towards the hydrido site, as shown by the relatively small O( 1)-Ru-P( 1) angle of 88.4 (2)O. This seems to result from close contacts between ring 1 and ring 5 which prevents P( 1) from moving closer to the hydrido ligand. The shortest such contact is C(ll)-H(52) at 2.52 A. The close approach of P( 1) and O( 1) is facilitated by the staggering of rings 1 and 3 with respect to 0 ( 1 ) as shown by the O(1)-Ru-P(1)-C(l1) and O(1)Ru-P( 1)-C(31) torsion angles about the Ru-P( 1) bond (see Table XI). This is also clearly shown in Figure 2. Although the angular parameters, and thus the spacial arrangements of the phosphine ligands, are similar in the above complexes there are notable differences in the Ru-P distances. In the methacrylate complex the mutually trans Ru-P distances (2.327 (3) and 2.31 1 (3) A) are significantly shorter than the unique cis Ru-P distance of 2.370 (3) A. This is the opposite to what is observed in the acetate and formate complexes where the cis Ru-P distances are shorter by ca. 0.127 and 0.083 A, respectively. It has been suggested62that in the formate complex the shorter Ru-P distance results from the lower trans influence of oxygen compared with phosphorus. However, Skapski and Stephens6I believe that the observed difference is too great to result merely from this difference in trans influence and suggest instead that if the acetate (or formate) ligand be viewed as occupying one coordination site, then the complex can be considered as quasi-five-coordinate. Hence the unique phosphine would occupy the apical position of a
& Figure 3. The inner coordination sphere of the molecule, including the entire n-butyl methacrylate ligand. Some relevant bond lengths and angles are shown. Vibrational ellipsoids are shown at the 50% level, except C(6), C(7), and C(8).
square pyramid with no trans competition for electrons, resulting in a short Ru-P distance. The coordination in the methacrylate complex is more nearly octahedral (the O( 1)Ru-C(l) angle is 75.6 ( 4 ) O compared with 57.6 (4)' and 55.0 (1 3)' in the acetate and formate complexes) so the trans ligand is more nearly opposed to the phosphine. By this criterion one would therefore expect a slightly longer cis Ru-P distance than in the quasi-five-coordinate complexes. However, clearly the largest effect is the strong trans influence of the vinyl carbon atom. Cetinkaya et al.63have compared the trans influence of several ligands in octahedral Rh(II1) systems, based on Rh-CI distances trans to the ligand in question and have established the order: a-alkyl > a-phenyl > t e r t - ~ a r b e n e>~s-carbene ~ > tert-phosphine > tert-phosphite > tert-arsine 7r-olefin > chlorine amine pyridine > ROH. Ru-C(1) can be classified as a secondary carbene linkage66since the bonding within the chelate is delocalized (this is discussed later) with the result that C(l)-C(2) is less than a formal double bond. Atom C( 1 ) therefore exerts the expected large trans influence with Ru-P(1) being 0.043 8, longer than Ru-P(2) and 0.059 8, longer than Ru-P(3). In this respect it is unusual that in R U H ( C ~ O H ~ ) ( M ~ ~ P C H ~ Cand H ~ PRuz(Me2PM~~)I~~ CH2CH2PMe2)421 the Ru-P distances trans to the coordinated
Yamamoto, Ibers, et al.
-
-
-
/ Addition of Alkyl Methacrylate to Ruthenium
3882 Table XI. Selected Angles (deg) in RuH(CHC(CH,)CO,C,H,)(PPh,),
P(?)-Ru-P(3) P( l)-Ru-P(2) P( 1)-R u -P( 3) P( 1)-Ru-C( 1) P(l)-Ru-O(l) P(2)-Ru-C(1) P(2)-Ru-O(1) P(3)-Ru-C(1) P( 3)-Ru-O (1) C(1)-Ru-O(l) RU-C( 1)-C(2) C( 1)-c(2)-c(4) C(l)-C(2)-C(3) C(3)-C(2)-C(4) C(2)-C(4)-0(1) C(2)-C(4)-0(2) 0(1)-C(4)-0(2) C(4)-0(1)-Ru C(4)-0(2)-C(5) 0(2)-C(5)-C(6) C(5)-C(6)-C(7)
152.50 (10) 99.62 (10) 99.30 (9) 164.0 (3) 88.4 (2) 84.6 (3) 108.0 (2) 82.6 (3) 92.3 (2) 75.6 (4) 117.8 (8) 113.4 (10) 126.5 (10) 120.0 (1 1) 121.2 (11) 118.6 (10) 120.1 (11) 111.6 (7) 116.8 (10) 114.5 (17) 71 (3)
Ru-P(l)-C(ll)-C(l2) R~-P(l)-C(21)-C(22) R~-P(l)-C(31)-C(32) R~-P(2)-C(41)-C(42) Ru-P(2)-C(5 1)-C(52) Ru-P(2)-C(6 1)-C(6 2)
-25.1 -24.4 79.6 53.8 78.5 24.2
C(6)-C(7)-C(8) Ru-P(l)-C(ll) Ru-P( 1)-C(21) Ru-P(l)-C(31) Ru-P(2)-C(41) Ru-P(2)-C(5 1) Ru-P(2)-C(61) Ru-P(3)-C(71) Ru-P(3)-C(81) Ru-P(3)-C(91) C(1 l)-P(l)-C(21) C(ll)-P(l)-C(31) C(21)-P(l)-C(31) C(41)-P(2)-C(5 1) C(41)-P(2)-C(61) C(51)-P(2)-C(61) C(71)-P(3)-C(81) C(7l)-P(3)-C(91) C(81)-P(3)-C(91)
121 (12) 113.7 (3) 123.4 (2) 113.7 (2) 110.2 (3) 119.4 (3) 121.3 (2) 116.7 (3) 119.9 (3) 114.6 (3) 101.2 (3) 99.0 (3) 102.5 (3) 101.8 (3) 100.7 (4) 100.3 (4) 95.7 (4) 102.2 (3) 104.7 (3)
Ru-P(3)-C(7 1)-C(7 2) R~-P(3)-C(81)-C(82) Ru-P(3)-C(91)-C(92) O(1)-RU-P(l)-C(l 1) 0(l)-R~-P(l)-C(31)
-10.2 41.1 77.5 63.2 -48.9
Torsion Angles (5) (8) (6) (5) (8) (7)
(7) (6) (8) (3) (4)
carbon atoms (2.301 (3) and 2.26 (1) A, respectively) are not The mode of coordination of the methacrylate ligand, which longer than the mutually trans Ru-P distances (2.303 (3), had been proposed on the basis of spectroscopic and chemical 2.280 (3); and 2.32 ( l ) , 2.28 (1) A, respectively). Even viewing evidence, has been confirmed by the x-ray determination. Thus Ru-C( 1) as a simple vinyl linkage, rather than a s a carbene the ligand is bidentate and is coordinated via the vinyl carbon linkage, the large trans influence is again expected. In two atom and the carboxyl oxygen atom. Although the location of other cr-vinyl complexes, tran~-PtCl(CH=CH2)(PEt2Ph)2~~ most of the atoms in this ligand was straight forward, the terand P ~ C ~ ( O - P ~ ~ P C ~ H ~ C = C H C ~the H ~Pt-CI PP~~O ) three , ~ ~atoms of the n-butyl group were located only apminal bonds trans to the vinyl carbon atoms (2.398 (4) and 2.377 (2) proximately owing to a disorder of these atoms. Viewing the A, respectively) are significantly larger than observed (2.294 packing diagram it is not difficult to imagine why this group is disordered, since it fits into a large cavity created by the (4) A) in tran~-PtCl2(P(CH2CH3)3)2~~ where the chloro ligands are mutually trans. phenyl rings from adjacent molecules, and has no obvious The trans Ru-P distances in the methacrylate complex, a t orientational preference. 2.327 (3) and 2.31 1 (3) A, are also unusually short. For exThe Ru-C( 1) bond, at 2.061 (10) A, is approximately what ample in other complexes containing meridional phosphine one would expect for a Ru-C single bond (2.06 A), based on ligands the trans Ru-P distances average 2.37 (2) A.61,62,70-72the covalent radii of R u and ~ C~ ( S P ~ )It. is~ also ~ comparable The distances in the present complex are actually closer to with several a-bonded Ru-C(sp2) distances reported,39,41*76-80 Ru-P distances which are cis, as for example in facranging from 2.01 (3) to 2.160 (10) A. It has been suggest[ R u ~ C I ~ ( P E ~ ~ P (average ~ ) ~ ] + 2.318 (7))70 and ed39,78,79that a Ru-C distance of this magnitude represents R u ( S C S H ~ N ) ~ ( P Pa t~2.319 ~ ) ~ (2) , ~ ~and 2.332 (2) A. some degree of multiple bond character. Indeed this distance Apart from the phenyl rings, the complex under study has in the methacrylate complex is among the shortest of such approximate mirror symmetry. However, the twisting of the distances observed. However, these distances are all longer phenyl groups about the P-C bonds destroys the opportunity than a Ru-C(isocyanide) distance79of 1.979 A8I and several for such symmetry. The steric interaction between the bulky Ru-C (carbonyl) distances ranging from 1.825 to 1.87 (6) PPh3 groups results in a wide range of torsion angles about the A.39,41,77,79,82 Although carbonyls function as good x accepP-C bonds, as is shown in Table XI. Ring 9 is approximately tors, isocyanide ligands are generally regardeds3qs4 as poorer parallel to the methacrylate chelate plane. However, its x acceptors. This suggests that in the present complex, based pseudo-mirror-related mate, ring 6, is approximately peron the Ru-C( 1) distance, C ( 1) is a poorer x-acceptor than the pendicular to this plane, resulting in close contacts between ring isocyanide ligand. 6 and the chelate (see Table X) and a corresponding increase The oxygen atom in the methacrylate ligand seems to be in the P(2)-Ru-O(1) angle over the P(3)-Ru-O(1) angle only weakly coordinated to the ruthenium atom. The Ru-O(1) (108.0 (2)' and 92.3 (2)O, respectively). The bulky triphendistance at 2.246 (7) 8, is comparable with the R u - 0 distances ylphosphines are obviously of paramount importance in dein the acetate6' (2.198 (13) and 2.210 (10) A) and the fortermining the overall geometry, as confirmed already by the mate62 (2.29 (4) and 2.23 (3) A) complexes. Since these lisimilarities between the methacrylate, acetate, and formate gands are replaced readily in solution they may be regarded complexes. The effect of the phosphines is further emphasized as weakly coordinated. In addition these R u - 0 distances by the similarities of the P-Ru-P angles in these six-coordinate are significantly longer than the sum of the covalent radii (1.99 complexes to those in the five-coordinate complexes A)74,85and are greater than several R u - 0 distances reported82,s6,87(ranging from 1.96 (2) to 2.103 (7) A). Thelong R u H C I ( P P ~and ~ ) R~ ~~C~l 2 ( P P h 3 ) 3 . ~ ' There are no unusual features in either the P-C distances, R u - 0 distance in the present complex probably results from the Ru-P-C angles, or the C-P-C angles in the present the large trans influence of the hydrido ligand. A similar structure. lengthening of the R u - 0 bond trans to H was observed in the Journal of the American Chemical Society
/
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3883 formate complex. However, in that quasi-five-coordinate References and Notes complex the small bite of the chelate results in both R u - 0 distances being long. (1) (a) Tokyo Institute of Technology: (b) Northwestern University. (2) A. D. Ketley, L. P. Fisher, A. J. Berlin, C. R. Morgan, E. H. Gorman, and T. Within the planar ring of the methacrylate ligand the disR. Steadman, lnorg. Chem., 6, 657 (1967). tances suggest delocalized bonding over the chelate framework (3) K. Maruya, T. Mizwoki, and A. Ozaki, Bull. Chem. Soc.Jpn., 46,993 (1973). with bond lengths generally being intermediate between single (4) J. M. Davidson and C. Triggs. J. Chem. SOC.A, 1324, 1331 (1968). (5) Y. Fujiwara, I. Mwitani, S.Danno, R. Asano, and S. Teranishi. J. Am. Chem. and double bond values. Thus C ( l)-C(2), a t 1.368 (15) A, SOC., 91, 7166 (1969). is slightly longer than one might expect for the C=C bond (6) R. F. Heck, J. Am. Chem. SOC., 90, 5535 (1968), and references therein. (7) R. F. Heck, J. Am. Chem. SOC.,91, 8707 (1969). (1.33 A). Similarly C(2)-C(4) is short (1.442 (1 5) A) for a (8) U. Klabunde and G. W. Parshall. J. Am. Chem. Soc., 94, 9081 (1972). single-bonded C-C distance (1.46 A) involving sp2 hybridized (9) E. K. Barefield, G. W. Parshall, and F. N. Tebbe, J. Am. Chem. SOC.,92, carbon atoms. The value of C(2)-C(3) (1.535 (15) A), exo 5234 (1970). (10) R. J. Hodges, D. E. Webster, and P. B. Wells, J. Chem. Soc., Dalton Trans., to the ring, is as expected. In addition the C(4)-0(1) distance 2577 (1972), and references therein. (1.254 (12) A) is very long for a C=O double bond, in (1 1) C. Masters, J. Chem. SOC.,Chem. Commun., 1258 (1972). (12) N. F. Goldshleger, M. J. Tjabin, A. E. Shilov, and A. A. Shteinman, Zh. Fiz. agreement with the low value found for vc 0 A comparison Khim., 43, 2174 (1969); Abstract of the 5th International Conference on with several other coordinated carboxyl groups verifies that Organometallic Chemistry, Vol. 1, 1971, p 328. C(4)-O( 1) has a bond order less than 2. In RuH(02CCH3)(13) J. L. Garnett and R. S.Kenyon, J, Chem. Soc., Chem. Commun., 1227 (PPh3)3,61 R u H ( O ~ C H ) ( P P ~R~ U ) ~~, (~ O ~ ~ C C ~ Hand ~ ) ~ C ~ ,(1971). ~~ (14) J. E. Bercaw, R. H. Marvich, L. G. Bell, and H. H. Brintzinger, J. Am. Chem. in which the C-0 bonds are SOC.,94, 1219 (1972). (15) J. E. Bercaw, J. Am. Chem. SOC.,96, 5087(1974). generally considered to be intermediate between single and (16) L. P. Seiwell, J. Am. Chem. SOC.,96, 7134 (1974). double bonds, the average C-0 distances are 1.259 (18), 1.25 (17) E. L. Muetterties and F. J. Hlrsekorn, J. Am. Chem. Soc., 96,4063 (1974). ( 6 ) , 1.27 (3), and 1.26 (3) A, respectively. Similarly in (18) J. Chatt and R. S.Coffey, J. Chem. SOC.A, 1963 (1969). (19) J. Chatt and J. N. Davidson, J. Chem. SOC.,843 (1965). R u ~ ( C O ) ~ H ( C I O Hthe ~ Ocoordinated ) C-0 bond measures (20) U. A. Gregory, S.D. Ibekwe, E. T. Kiibourn, andD. R. Russel, J. Chem. Soc. 1.259 (13) A.82The C(4)-O( 1) bond in the present complex A, 1118(1971). (21) F. A. Cotton, B. A. Frenz, and D. L. Hunter, J. Chem. Soc., Chem. Commun.. is, however, considerabl shorter than the coordinated C-0 755 (1974). distance (1.318 (10) in Pt(PPh3)2(PhCON2COPh)88 (22) W. Keim. J. Organomet. Chem., 14, 179 (1968); 19, 161 (1969). showing that it maintains a significant component of multi(23) G. W. Parshall, Acc. Chem. Res., 3, 139 (1970). (24) R. A. Schunn, lnorg. Chem., 9, 2567 (1970). plicity. Carbonyl distances in which this group is not coordi(25) J. M. Duff, B. E. Mann, 8. L. Shaw, and B. Turtle, J. Chem. SOC..Dalton nated have been observed in the range 1.19 (2) to 1.223 (10) Trans., 139 (1974), and references therein.
x)
A.65.88.89
Exo to the chelate ring, the C(4)-0(2) bond (1.327 (1 3) A) in the ester linkage is shorter than might be expected but the 0(2)-C(5) bond a t 1.45 (2) A is normal. Other distances within the n-butyl group are not reliable because of the disorder problem. The overall geometry of this group is, however, clear. As mentioned previously the 'H N M R signal from the vinylic proton is a t very low field (8.2 ppm) compared with two other complexes with coordinated vinyl groups (4.86 and 1.58 ppm),33,35suggesting that the chemical shift of this proton is very sensitive to the electronic environment of the metal, Indeed in the present complex this proton (H( 1)) is only 2.81 8, from the R u atom. The coordination mode of the vinylic entity might also be important, since in the chelated form the possibility of delocalization leading to ring currents within the chelate which might deshield this proton must be considered. The closest approach of an ortho-hydrogen atom of the phenyl groups to the Ru atom is Ru-H( 12) at 3.07 A.
Conclusions Detailed spectroscopic and chemical studies of a seemingly simple a-olefin complex, as judged from its composition alone, have revealed that a new hydrido-alkenyl type complex was formed by oxidative addition involving C-H cleavage of alkyl methacrylate to a zero-valent ruthenium complex. The x-ray crystallographic analysis of the n-butyl methacrylate complex confirms the molecular structure proposed on the basis of spectroscopic and chemical evidence. The behavior of this type of complex, as demonstrated by introduction of a methyl group into a @-positionof the alkyl methacrylate, suggests a variety of synthetic applications. Acknowledgments. This work was kindly supported by the
US.National Science Foundation and the Ministry of Education of Japan. M.C. wishes to thank the National Research Council of Canada for a Postdoctoral Fellowship. Supplementary M a t e r i a l Available: T h e tables of observed and calculated structure amplitudes, the idealized phenyl H positions (Table VIII), and root-mean-square amplitudes of vibration (Table IX) (38 pages). O r d e r i n g information i s given o n any current masthead page.
(26) B. N. Cockburn, D. V. Howe. T. Keating. E.F. G. Johnson, and J. Lewis, J. Chem. SOC., Dalton Trans., 404 (1973). (27) N. Ahmad, E. W. Ainscough, T. A. James, and S.D. Robinson, J. Chem. SOC.,Dalton Trans., 1151 (1973). (28) C. Masters, J. Chem. SOC.,Chem. Commun., 191 (1973). (29) M. I. Bruce, B. L. Goodall, and F. G. A. Stone, J. Chem. SOC.,Chem. Commun., 558 (1973). (30) A. C. Jarvls, R. D. W. Kemmltt, B. Y. Kimura, D. R. Russel, and P. A. Tucker, J. Organomet. Chem., 66, C53 (1974). (31) M. A. Bennett, R. N. Johnson, and 1. B. Tomkins, J. Am. Chem. SOC.,96, 61 (1974), and references therein. (32) M. G. Clericl, S. DiGioacchino, F. Maspero, E. Perrottl, and A. Zanobl, J. Organomet. Chem., 64,379 (1975). (33) J. M. Kllegman and A. C. Cope, J. Organomet. Chem., 16, 309 (1969). (34) R. J. Foot and B. T. Heaton, J. Chem. SOC.,Chem. Commun., 838 (1973). (35) J. F. van Baar, K. Vrleze, and D. J. Stufkens, J. Organomet.Chem., 85, 249 (1975). (36) S.Komiya and A. Yamamoto, Chem. Leff., 475 (1975). (37) C. Glannotti and M. L.H. Green, J. Chem. SOC.,Chem. Commun., 1114 (1972). (38) K. Elmitt, M. L. H. Green, R. A . Forder, I. Jefferson, and K. Prout, J. Chem. SOC.,Chem. Commun., 747 (1974). (39) A. Cox and P. Woodward, J. Chem. SOC.A, 3599 (1971). (40) M. i. Bruce, M. A. Cairns, and M. been, J. Chem. Soc., Dalton Trans., 1293 (1972). (41) M. Evans, M. Hursthouse, E. W. Randall, E. Rosenberg, L. Milone, and M. Valle, J. Chem. SOC., Chem. Commun., 545 (1972). (42) A. J. P. Domlngos, E.F. 0.Johnson, and J. Lewis, J. Organomet. Chem., 36, C43 (1972). (43) A. J. Canty, A. J. P. Domingos, B. F. G. Johnson, and J. Lewis, J. Chem. SOC.,Dalton Trans., 2058 (1973). (44) A. J. Deeming and M. Underhill, J. Chem. SOC.,Dalton Trans., 1415 (1974). (45) J. B. Keister and J. R . Shapiey, J. Organomet. Chem., 85, C29 (1975). (46) J. J. Levlson and S.D. Robinson, J. Chem. SOC.A, 2947 (1970). (47) T. Ito, S.Kltazume, A. Yamamoto, and S.Ikeda, J. Am. Chem. SOC.,92, 3011 (1970). (48) The abbrevlation PPh3-de Is used to mean the trlphenyiphosphine ligand where all SIXortho-protons are deuterated. Other abbrevlations used are: Ph, phenyl; Me, methyl: Et, ethyl: CPr, isopropyl: n-Bu, n-butyl. (49) E. R . H. Jones, T. Y. Shen, and M. C. Whlting, J. Chem. SOC.,230 (1950). (50) W. H. Knoth, J. Am. Chem. Soc., 90, 7172 (1968). (51) R. J. Doedans and J. A. Ibers, lnorg. Chem., 6, 204 (1987). (52) The Northwestern absorption program, AGNOST, includes the CoppensLeiserowitz-Rablnovich loglc for Gaussian Integretlon. In addltion to various local programs for the CDC 6400 computer, modlfled versions of the following programs were employed: Zalkin's FORDAP Fourier summation program, Johnson's ORTEP thermal ellipsoid plottlng program, and Busing and Levy's ORFFE error function program. Our full-matrix, least-squares program, NUCLS, In its nongroup form, closely resembles the Buslng-Levy ORFLS program. (53) D. T. Cromer and J. T. Waber, "International Tables for X-Ray Crystallography", Vol. IV, Kynoch Press, Birmingham, England, 1974, Table 2.2. For hydrogen atoms see R. F. Stewart, E. R. Davldson, and W. T. Slmpson, J. Chem. Phys., 42, 3175 (1985). For the values of A f and A f ' for Ru and P see D. T. Cromer and D. Liberman, J. Chem. Phys., 53, 1891 (1970). (54) See paragraph at end of paper regardlng supplementary materlai. (55) S.Komlya, A. Yamamoto, and S. Ikeda, J. Organomet. Chem., 42, C65
Yamamoto, Ibers, et al.
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Addition of Alkyl Methacrylate to Ruthenium
3884 (1972). (56)S.Komiya, A. Yamamoto, and S . Ikeda. Bull. Chem. Soc. Jpn., 48, 101 (1975). (57)A. Yamamoto. T. Yamamoto, T. Ito, S.Komiya. A. Miyashita, T. Ikariya, T. Saruyama, M. Kubota. and Y. Nakamura, 7th International Conference on Organometallic Chemistry, Abstracts, p 133, 1975,Venice, Italy. (58)M. Imoto. T. Otsu. and Y. Harada, Makromol. Chem., 65, 180 (1963). (59)H. Bonneman, Angew Chem., 82,699(1970). (60)S.Komiya and A. Yamamoto. Bull Chem. SOC. Jpn.. in press. (61)A. C. Skapski and F. A. Stephens, J. Chem. Soc.,Dalton Trans., 390 (1974). (62)(a)A. I. Gusev, G. G. Aleksandrov, and Y. T. Struchkov, Zh. Strukt. Khim.. 14,685 (1973);(b) J. Struct. Chem., 14,633 (1973):(c) I. S.Kolomnikov, A. I. Gusev, G. G. Aleksandrov, T. S.Lobeeva, Y. T. Struchkov,and M. E. Vol'pin, J. Organomet. Chem., 59,349 (1973). (63)B. Cetinkaya, M. F. Lappert, G. M. Mclaughlin, and K. Turner, J. Chem. Soc., Dalton Trans., 1591 (1974). (64)The tertcarbene was added to this series afterwards by M. Cowie et al.; see ref 65. (65)(a)M. Cowie. J. A. Ibers. Y. Ishii, K. Itoh, I. Matsuda, and F. Ueda, J. Am. Chem. SOC., 97, 4748 (1975);(b) M. Cowie and J. A. Ibers, lnorg. Chem., 15, 552 (1976). (66)D. J. Cardin, B. Cetinkaya, and M. F. Lappert, Chem. Rev., 72,545 (1972). (67)C. J. Cardin, D. J . Cardin, M. F. Lappert, and K. W. Muir. J. Organomet. Chem., 60, C70 (1973). (68)G. B. Robertson and P. 0. Whimp, lnorg. Chem., 13,2082 (1974). (69)G. G. Messmer and E. L. Amma, lnorg. Chem., 5, 1775 (1966). (70) K. A. Raspin, J. Chem. Soc. A, 461 (1969). (71)S.J. La Placa and J. A. Ibers, lnorg. Chem., 4,778 (1965).
(72)A. C. Skapski and P. G. H. Troughton, Chem. Commun.. 1230 (1968). (73)S.R. Fletcher and A. C. Skapski, J. Chem. Soc., Dalton Trans., 635 (1972). (74)J. P. Jesson and E. L. Muetterties, "Chemist's Guide Basic Chemical and Physical Data", Marcel Dekker, New York, N.Y., 1969,pp 2-3. (75)F. A. Cotto; and G. Wllkinson, "Advanced lnorganlc Chemistry", 2d ed, Interscience, New York, N.Y., 1966,p 105. (76)T. Blackmore, M. I.Bruce, and F. G. A. Stone, Chem. Commun..852 (1971). (77)R. Belford, H. P. Taylor, and P. Woodward, J. Chem. Soc., Dalton Trans., 2425 (1972). (78)R . J. Sundberg, R. F. Bryan, 1. F. Taylor, Jr., and H. Taube, J. Am. Chem. SOC., 96, 381 (1974). (79)D. F. Christian, G. R. Clark, and W. R . Roper, J. Organomet. Chem., 81, C7 - . I,I.R- 7. d.,\. (80)M. I. Bruce, R. C. F. Gardner, B. L. Goodall, and F. G. A. Stone, J. Chem. SOC.,Chem. Commun., 185 (1974). (81)No standard deviations are given in the paper. (82)A. J. P. Domingos, 6.F. G. Johnson, J. Lewis, and G. M. Sheldrick, J. Chem. Soc., Chem. Commun., 912 (1973). (83)A. C. Sarapu and R . F. Fenske. lnorg. Chem., 11, 3021 (1972). (84)P. M. Treichel, Adv. Organomet. Chem., 11, 21 (1973). (85)L. Paullng, "Nature of the Chemical Bond", 3rd ed. Cornell University Press, Ithaca. N.Y., 1960,p 224. (86) M. J. Bennett, K. G. Cauiton, and F. A. Cotton, lnorg. Chem., 8, 1 (1969). (87)F. A. Cotton, J. G. Norman, A. Spencer, and G. Wilkinson, Chem. Commun., 967 (1971). (88)S. D. lttel and J. A. Ibers, Inorg. Chem., 12,2290 (1973). (89)A. Braibanti. A. Tiripicchio, A. M. Manotti Lanfredi, and M. Camellini, Acta Crystallogr., 23, 248 (1967).
Quenching of Triplet States by Inorganic Ions. Energy Transfer and Charge Transfer Mechanisms A. Treinin' and E. Hayon* Contribution from the Pioneering Research Laboratory, U S . Army Natick Laboratories, Natick, Massachusetts 01 760. Receiued August 4, I975
Abstract: T h e effect of inorganic anions on the triplet states of aromatic hydrocarbons and carbonyl compounds ( M ) in aqueous solution a t room temperature was investigated using the fast-reaction techniques of flash and laser photolysis. T h e results have been interpreted on the basis of two major quenching mechanisms: energy transfer and charge transfer. Typical T-T energy transfer was demonstrated for NOz-. Its triplet energy was also determined and found to be ET = 53 i 2 kcal/mol. T h e very fast quenching of triplet acetone by NCS- may also involve energy transfer. In other cases, the quenching r a t e constant k , was found to depend largely on the proximity of the CT level of the M-anion complex to the triplet level of M. T h e energies of such CT levels were calculated from the thermodynamic properties of the species involved. T h e dependence of k , on AECT = Ec- - E M *was examined when M* is either a singlet S I or a triplet T I excited state. For the systems examined, the analysis reveals that SI and TI states a r e quenched by inorganic ions via similar mechanisms, and in both cases k , becomes diffusioncontrolled when l E c 5~ 0. However, with the exception of S032-, no chemical reactions were found t o result from the quenching reaction. Possible reasons for this behavior a r e discussed. In some of the systems where quenching was slow, minor reactions did take place and could be ascribed to redox interactions with radical ions (or their hydrolysis products) produced from the photoionization of the aromatic molecules, and not to a direct reaction of the ions with the triplet states. Evidence for such a photoionization was provided in a detailed study of naphthalene photolysis in water, and its mechanism is discussed.
I. Introduction Quenching of excited singlet states by simple diamagnetic anions has been studied extensively through fluorescence measurements, and various mechanisms have been proLittle is known, however, on the corresponding quenching of triplet states, and it was even concluded that diamagnetic ions hardly have any effect.' Some early indications, however, bear evidence to the opposite, e.g., a work8 on the quenching of fluorescein type dyes with I-. More recently this problem was studied for anthraquinone triplets by flash photolysisg and very efficient quenching by anions was reported involving, i n some cases, net electron transfer reactions with the formation of inorganic radicals and the semiquinone. There is new evidencelo that these results may be incorrect and that the transient species studied were not the triplets. Recently, Journal of the American Chemical Society
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the quenching of triplet pyrazine by inorganic anions has been investigated by laser photo1ysis.I' From their studies on triplet quenching by transition metal ions and their complexes, Linschitz et al.I2 reached the following conclusions: (a) diamagnetic ions can act as efficient quenchers; (b) there is no essential difference in mechanism between the quenching of excited singlets and triplets; (c) charge transfer states appear to play an important role. For the quenching and photoreduction of carbonyl triplets by amines this role is now reasonably well e s t a b l i ~ h e d ,but ' ~ with simple anions as quenchers the picture is unclear even in the case of singlet quenching. In his recent work^^^,^ Watkins has presented serious arguments against the charge transfer mechanism although he still emphasizes the role of some kind of coupling with CT states. He also investigated the quenching of biphenyl, naphthalene, and anthracene triplets by I-, NCS-,
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