METALCARBONYL-PHOSPHORUS TRIPLUORIDE SYSTEMS1801
VoL 7, No. 9, Se$ternber i968
Mn I
moieties for electron density.] In keeping with this proposal, i t may be noted that the mean Mn-CO bond distance in other compounds (where there is competition for a-electron density) is greater, viz., 1.823 8 in Mnz(CO)lo,601.823 in HRe2Mn(C0)14,51and 1.836 A in HMn(C0)6.sz Discussion The results of the present structural analysis would appear to strengthen our previously stated ideasI7 on the reaction of azulene with transition metal carbonyls. If the initial reaction prQduces an intermediate such as V, then the present complex trans-CloHsMnz(CO)e (VI) and the [C10H8Mn(C0)3]2 of Burton, et aL3 (VII), are to be expected as products. The particular factors that favor the formation of gne product rather than the other have yet to be determined, but it would seem likely that manganese-rich VI will be preferentially formed in solutions containing an excess of dimanganese decacarbonyl, while dimeric VI1 will form in solutions containing an excess of azulene. However, the limited stability of VI1 as compared to VI will complicate the over-all pattern. Intermolecdar Contacts Figure 6 shows the packing of molecules within the crystal lattice. Quantztative data on intermolecular interactions are collected in Table VIII. There are no (50) L. F. Dah1 and I IION,\I,,L,
Inorganic Chenzistty
J . CLARK
The trifluorophosphine substitution species of nianganese pentacarbonyl hydride are all colorless liquids which have vapor pressures of the order of 20 torr a t ambient conditions. The approximate melting ranges are shown in Table I. Since these materials appear to become glassy solids rather than crystalline, it is not certain what significance can be connected with these ranges. As the degree of PF3 substitution increases, the stability of the intermediates with respect t o air oxidation increases. The parent EMn(CO)6 reacts rapidly with air at -78" and becomes dark red. The monosubstituted intermediate colors more slowly than the parent a t -78". The disubstituted complex slowly turns yellow in air at room temperature while the higher substituted species show no evidence of air oxidation. The complete series of hydrides is thermally stable under ambient conditions when they are sealed in evacuated ampoules. Attempts to resolve the expected geometric isomers for the intermediate species (assuming either a pentacoordinate or octahedral structure) did not succeed. Nine columns mere tried in an attempt to bring about separation of the isomers. Forecuts and tailcuts of each chromatographic peak showed the same infrared patterns. This implies that the peak is composed of only one compound. If two components were in one peak, there would probably be some degree of separation even though the peak may appear symmetrical. The probability that geometric isomers will have exactly identical retention volumes, so that they appear homogeneous, is extremely small. I n contrast to what is norinally encountered with substituted metal carbonyls, the infrared spectra are of little value in giving definitive identification of the individual species. Frequently, when simple substitution takes place in mononuclear metal carbonyls, group theory will not only allow one to distinguish betn-een various isomeric possibilities, but it will give the first experimental clues as to the actual degree of substitution. However, this is not found in the present case. The infrared spectra are shown in Table 11. The hydride bands of the various species occur in the 17801850-cm-l region, are weak and broad (about 20 cm-l a t half-height), and shift progressively about 9-12 cm-' to higher frequency for every degree of substitution. This band shows more clearly than the hydrogen analysis that the species are indeed hydrides. The gas spectrum of a typical hydride mixture in a DC1 atmosphere showed a slow weakening in intensity of the 1800-cm-' hydride band and the appearance of the deuteride stretch a t about 1290 cm-'. This reconfirms the fact that the stretch a t about lS00 cm-' belongs to a hy$ride atom. The only absorptions in the ir region of 4000-700 cm-1 other than hydride bands are found in the 21251930- and 800-950-~m-~regions characteristic of terminal carbonyls and PF3groups, respectively. Spectra of HMn(C0)3(PF3)2 which are characteristicof the whole series are shown in Figure 1. However, closc examination of the carbonyl region
11
'I'AHLE
ISYRARED SPECTRA OF 'THE HYDRIDE-SUBSTITUTIOS SERIES (cM-.l ) H M nHMn(COh (CO)af,PF3) 2118 v w 2101 w 2113 sh 2045sh 2046 w 2035 m 2017 vvs 2016 vs 2008 s h 2009 sh 1985 vw' 1982 w' 1967 v w U 1968 vwU 1780 vw
HRfnHMnHXn(CO)a(PF3)2 'CO)?(PF3)3 ( C O )(PPr)a 2086 rn 2071 vvw 2038 vs 2076m 2058w 2011 m 2031 m 2032 w 1989 V I V ~ 2027 m 2023 w 2011 vvs 2007 vs 1976 w" 1Y75 v w u 1969 vwu 1964 vw"
1790 v w
1806 vw
1823 v w
1838 v w
lk46 v w
897 m 888 s 875 s 867 sh
'311 rn 889 s 884 sh 882 rn 873 m 663 s 855 sh
021 rn $102s 890 s 873 5 858 s 852 sh
041 m 908 s 902 sh 882 m 889 yi' -858 s 851 m
'362 v
n
u14 vc '306 vs YO1 s h 880 v w
868 sh 857 s a49 rn
Probable CI3stretches. Cm 2100
2000
1900
-1.
1800
900
800
Figure 1.-Infrared spectra of H M I I ( C O ) ~ ( I ' F i~l l ) ~Iicxane. Coiiceritratioris: 7 aiid 0.ir1/'00 rl of hexane.
sh0n.s that the spectra are not characteristic of any single species that might be expected. As an example, the material clearly shown to be monomeric and of a composition H M n ( C 0 ) (PF,), has three carbonyl stretching frequencies: 2038 (vs), 2011 (m), and 1989 (vw) cm-'. The 1989-cm-l vibration can be attributed to a CI3mode, but the medium-strong 2011-cm-' vibration is too intense to be so assigned. For one single monomeric monocarbonyl, there can obviously be only one fundamental stretching vibration. Thus one is forced to conclude that there is either an extra source for absorption in this region or that there is more than one isomer present. This general pattern of excess absorptions is observed with all of the intermediate species. In order to shed some light on these questions, phosphorus trifluoride substitution into other related manganese compounds has been studied. The geometric isomers of HC2F.,Mn(CO)4(PF3) haw been produced by two reaction procedures. In the first, the two species are just two of several products in the uv reaction betxveen HC2F4Mn(CO)r,and PF:j which are isolable by glpc. I n the second, they were the sole products of the reaction between HMn(C0)*(PF,) and C2F4. The identity of the two products produced by the two routes in itself essentially proves the composition of the species. The fact that these two compounds are produced simultaneously and are the first reaction products from the interaction between
Vol, 7 , No. 9, September 1968
METALCARBONYL-PHOSPHORUS TRIFLUORIDE SYSTEMS 1805
HC2F4Mn(CO)6and PF3 further confirms the composition. Thus in this system as in the molybdenum species, geometric isomers are readily isolated. The infrared spectra of the HC2F4Mn(C0)4(PF3) species shown in Table 111 add further confirmation to the identification of the compounds. Strong absorption occurs only in regions attributable to P-F, C-F, and C-0 groups. I n the carbonyl region, four and only four major absorptions occur for these two carbonyl compounds.
Some of the extra, weak bands a t low frequency can be attributed to CI3 modes, but the weak bands a t the higher frequency cannot be assigned in that fashion. It does not seem too reasonable that these are combinations or overtones arising from P-F absorptions. Since the P-F stretching modes occur below 950 cm-l, the combinations or overtones should not appear as high as the carbonyl region. I n addition, such values have never been observed in other PF3systems.lP2
Discusqion
Experimental evidence which has been presented in TABLE I11 the preceding sections shows that the hydrogen atom INFRARED SPECTRA OF THE GEOMETRIC has a very unusual role in manganese pentacarbonyl hyISOMERS OF K C n F I M n(CO)a(PFa) (CM - l ) dride and its trifluorophosphine derivatives. Contrary HC?RMn(CO)a(PPs)----Infrared region Isomer a Isomer b to the theory that the hydride is buried in the manC-0 str 2116 m 2071 V V W ganese electron cloud and therefore regarded as 2106 sha 2065 vvw a pseudo-iron complex, the hydride certainly must in2061 s 2040 vs fluence the stereochemistry of the complex. However, 2038 vs 2009 vw the present work also shows that these complexes 2013 vs 1982 VW5 probably should not be represented as rigid geometric 1970 V W " entities. The evidence implies that the properties of the hydride may be a compromise of the contrasting 1352 w 1352 w C-F 1173 vw 1097 rn theories concerning its stereochemistry. 1097 m 1083 rn It has been shown that the manganese carbonyl hy1081 w 1013 m dride substitution compositions are isolated in very high 1013 m 997 rn purity. However, ea,ch derivative possesses more 986 w fundamental carbon: 1 vibrations than are allowed by P-F str 915 m 887 s group theoretical considerations. These extra bands 903 rn 877 s cannot readily be attributed to any type of coupling 882 s or mixing phenomenon. Disproportionation or deProbable CI3 stretches. composition does not occur while the infrared spectrum of each compound is being determined. It must, Thus these fluoroalkyl species contrast strongly with therefore, be assumed that all of the carbonyl vibrathe hydrides in that the isomers of the former system tions arise from only the trifluorophosphine-substituare readily isolable and extra bands do not appear in the tion compositions. It is concluded that these extra carbonyl region. bands must indicate the presence of nonseparable I n the reaction between CF3COMn(C0)6and PF3, geometric isomers in each composition. enough work has been done so that a similar statement Phosphorus trifluoride derivatives of other metal can be made about the isolability of the isomers. This carbonyls do not consistently exhibit rigid geometric applies to both the acetyl compounds and the decarproperties. Geometric isomers are found for each PF3bonylated trifluoromethyl series. Greater detail will composition of the octahedral complexes be reported later concerning these R ~ M ~ I ( C O ) ~ - P Fsubstituted ~ of molybdenum, l1 chromium,12 and tungsten hexasystems. carbonyls.12 Substitution products of five-coordinated A considerable amount of effort has been expended in complexes, however, such as iron p e n t a ~ a r b o n y l lan ~ order to eliminate sources for the extra bands in the cobalt tetracarbonyl hydrideI4 do not contain separable carbonyl region of the hydride species other than nongeometric isomers. These intermediates also have separable isomers. This was done to show that these more carbonyl vibrations in their infrared spectra than bands are not due to volatile or nonvolatile impurities group theory arguments predict. The existence of too caused by such reactions as disproportionation, polymmany bands in the PF3 substitution series of Fe(CO)j erization, partial oxidation, etc., during the handling has been interpreted to be a result of a mixture of nonof the species. Analytical chromatograms of solutions separable geometric isomers l 3 It is suggested that the from which spectra have been obtained show the presgeometric isomers are undergoing rapid internal inverence of only solvent plus the original compound, No sion so that physical separation is impossible. other volatile species are seen. The gas-phase spectra It is now postulated that manganeze pentacarbonyl are essentially identical with those of the liquid phase hydride and its PFs-substitution products may also except for a small frequency shift. This shows that undergo a rapid internal inversion so that the geometric nonvolatile species have not made any contribution. isomers of each composition would not be separable. Since vacuum manipulation can be air free, this elimi(12) I
