Communications to the Editor
223 1 the mass spectra. The characterization data for 8 resembles those of 7; so this data has not been presented. Compound 8 has an observable parent ion. The appearance of the parent ion minus one carbonyl as the highest mass ion is not unexpected: M. R. Litzow and T. R. Spalding. "MassSpectrometry of inorganic and Organometallic Compounds", Elsevier, Amsterdam, 1973. D. F. Shriver, Acc. Cbem. Res., 3, 231 (1970). M. Cooke, M. Green, and D. Kirkpatrick, J. Cbem. SOC.A, 1507 (1968). M. Crutchfield, C. H. Dugan. J. H. Letcher, V. Mark, and J. R. Van Wazer, Top. Pbos. Cbem., 5, 230 (1964).
(JHCNP = 5.5 Hz) (re1 intensity 4), and a cyclopentadienyl proton singlet at 4.57 ppm (re1 intensity 5). Compound 9 shows 'H resonances centered at 2.04 ppm with overlapping multiplet structure which has not been fully resolved. The l3C{lH]N M R spectrum (THF, 32 O C , Me+% external standard) of 7 shows a methyl doublet a t 33.55 ppm (downfield) ( J C N P= 9.0 Hz), a methylene doublet a t 57.70 ppm (JCPN = 4.0 Hz), a Cp ring singlet at 87.73 ppm, and a carbonyl singlet a t 215.22 ppm. The spectrum of 9 shows a methyl multiplet (unresolved) a t 35.67 ppm, a methylene multiplet a t 53.85 ppm, and a carbonyl singlet a t 214.75 ppm. The compositions of 7,8, and 9 are established by elemental analyses and/or mass spectra. Furthermore, the reaction stoichiometry and characterization data are consistent only with the following equations CH3NCH2CH2N(CH3)PF
+ NaMo(C0)3(n-C5H5)
TH F
Iron Carbonyl Complexes Containing Positively Charged Phosphorus Ligands
NaF
+ [CH3fiCH2CH2N(CH3)P][ M O ( C O ) ~ I I - C ~ H ~(a)) ] 7 2CH3NCH2CH2N(CH3)PF
+ NazFe(CO)4
THF
R. W. Light, R. T. Paine* Department of Chemistry, University of New Mexico Albuquerque, New Mexico 871 31 Received June 9. I977
Sir: A 1972 paper by Fleming, Lupton, and Jekot' described a cyclic cationic phosphorus species 1. A more recent paper from
2NaF
+ [CH3NCH2CH2N(CH3)Pl2[Fe(C0)41
(b) 9 The structures of these unusual coordination complexes are now of central interest and the N M R and infrared data outlined here are consistent with the schematic arrangements shown here. We propose the structure of 7 in analogy to the
proposed structure of the mononuclear bis(pentafluor0pheny1)phosphine-metal carbonyl complexes reported by Green and coworkers.12 The structural possibilities for 9 are most interesting. The second-order 31PN M R pattern and the coupling constant and chemical-shift parameters suggest that the iron center is asymmetrically positioned between the two phosphorus coordination sites of the condensed diphosphine, but it is not yet clear if the iron atom is primarily associated with only one phosphorus atom as schematically shown here. X-ray crystal structure analyses of these compounds are in progress, and their structures and photochemistry will be presented separately.
Acknowledgments. The support of the University of New Mexico Research Allocations Committee is gratefully acknowledged. An N S F Grant MPS-06111 facilitated the purchase of the Nicolet FT N M R data system used in this work. The authors wish to acknowledge the assistance of Professor U. Hollstein in obtaining the mass spectral data, and numerous fruitful discussions with Professor S. Fleming.
I
this laboratory2 described the related noncyclic cations, [ [ ( C H ~ ) Z N ] ~ Pand ] + [(CH3)2NPCl]+. It was recognized in very early studies of these systems that the presence on phosphorus of (1) a free-electron pair, (2) a positive charge, and (3) a vacant p orbital should make ligands of this type effective a-type Lewis acids as well as weak C-type Lewis bases. These arguments are supported by the observation that the cyclic cation (1) will slowly displace C O from Fe(C0)s in accordance with eq 1.
[liCH,iNCHICHiscCH,)P:] -
+
[PF,]-
+
Fe(C0);
2 a
Fe,(CO), can also be used.
An alternative procedure for generating 2 involves the preparation of the easily characterized, stable compound, 3. Fluoride can be removed from this species by a Lewis acid such as PF5 to give 2. The appropriate reaction is given in eq 2. The
References and Notes (1) S. Fleming, M. K. Lupton. and K. Jekot, Inorg. Cbem., 11, 2534 (1972). (2) R. W. Kopp, A. C. Bond, and R. W. Parry, Inorg. Cbem., 15, 3042 (1976). (3) C. W. Schultz and R. W. Parry, Inorg. Cbem., 15, 3046 (1976). (4) M. G. Thomas, C. W. Schultz, and R. W. Parry, Inorg. Cbem., 18, 994 (1977). (5) E. R. Alton, R. G. Montemayor, and R. W. Parry, Inorg. Cbem., 13, 2267 (1974). (6) Neutral metal carbonyls undergo carbonyl displacement in the presence Of acyclic phosphine cations: R. W. Parry, personal communication. (7) Analyses of 8 and 9 were plagued by minor decomposition impurities. The analytical composition of these compounds must for now be deduced from
0002-7863/78/1500-223 1$01.OO/O
3
2
process is equally effective for preparing the analogous noncyclic3 cationic species [ [(CH3)2N]2PFe(CO)4]+ (4). A recent x-ray study of 3 in this laboratory4 has shown unambiguously that the molecule has trigonal-bipyramidal geometry and that the phosphine is in the axial position around Fe. The structure 0 1978 American Chemical Society
2232
Journal of the American Chemical Society
1 I00:7 / March 29, I978
Table I. Vibrational Spectral Data for Bis(dimethy1amido)fluorophosphine Iron Tetracarbonyl (Cyclic and Noncyclic) and the Phosphine Iron Carbonyl Cations Derived from Them (C-0 Stretching Region and P-F Stretching and Bending Region)
Fe(CO), (21 14)e (2031) 2027 1994 (1 984)
Substituted metal carbonyls (neutral) Cyclic ligand" Koncyclic ligandb iron carbonyl, iron carbonyl, cm-I m-I 206 1 1996
2055 1983
f
f
1949 19569 1931g 780
1951 1957g 1941 1938g
Cyclic ligand' cation carbonyl, cm-' 2121 2070
Metal carbonyl cations Noncyclic ligandd cation carbonyl, cm-l 2123 2063
f
2018, 1955h
f
2014, 1973h
805
Assignment (see ref 6)
AI ~ c o (equatorial ~ ~ ~ ) AI' VCO(sym) axial Az VCO(asyrn) axial E ~ c o ( equatorial ~ ~ ~ ~ ) of ligand [PF6]8PF LPF.51UPF
840 560
847h (VS)
563
UPF
Formula of compound is (CH,)hCH2CH2N(CH3)P(F)Fe(C0)4. Formula of compound is [(CH3)2N]2P(F)Fe(CO)a. Formula [ ( C H ~ ) & C H Z C H ~ N ( C H ~ ) P F ~ ( C OFormula ) ~ ] + . [((CH,)zN)2PFe(C0)4]+. e Values in parentheses were seen in Raman. f The A2 mode does not exist for LFe(C0)d g Spectra of dry solid films A Nujol mull sample of KPF6 gave peaks at 840 and 560 cm-l. Table 11. NMR Data" for Cyclicb and NoncyclicC( R ~ N ) z ( F ) P - F ~ ( C O and ) ~[(RzN)zPFe(C0)4]+ [PF,]-
Nucleus 3'P (relative tO
Temp, O C
-70
H3P04)
CycIicd d, -185 (JPF = 1162)
Noncyclice d, -193 JPF= 1073)
-70 I9F (relative to CFC13)
25
d, 7.3 ( J P F= 1165)
-300
S,
-31 1
Assignment P coordinated to Fe(C0)4 group P Of iPF6]-
d, -48.7 (JPF= 1085)
d, 71.3 d, 71.2 (Jp~=715) (Jp~z715)
-80' -10
S,
NoncyclicC
sept, 144 sept, 144 (Jp~=715) (Jp~z715)
Below 'H (relative to Me4Si)
Cyclicb
d of d, 2.86 (JPH = 13.3, JFH= 2.5) m, 3.33
d of d, 2.71
d, 3.05 ( J P H = 14.0)
( J P H = 10.8, J F H = 2.5)
F on coordinated (R2N)ZPF F of [PF6]-
d, 3.10 H of -CH3 (JPH = 11.1)
d, 3.83 (JPH = 8.0)
-CH2 of cyclic svstem
The formula of the I n d (parts per million) ( J in hertz). The formula of the cyclic cation is [(CH~)NCHZCH~N(CH,)~!'F~(CO)~]+. I
noncyclic cation is [((CH,)zN)2PFe(C0)4]+. The formula is (CH3)kCH2CH2N(CH3)P(F)Fe(C0)4. e The formula is ((CHdzN)2P(F)Fe(C0)4. resembles that published for Ph2HPFe(C0)4 by Kilbourn, Raeburn, and T h o m p ~ o nSimilarities .~ between solid-state and solution I R spectra for 3 indicate that the structures in solution and in the solid state a r e the same. This same structural conclusion for LFe(C0)4 (L is either the cyclic or noncyclic amidofluorophosphine ligand) is reached on the basis of an infrared spectral analysis which uses the excellent paper of Darensbourg, Nelson, and Hyde6 as a key. An earlier study3 had assigned equatorial phosphine geometry to [(C2H5)2N]2P(F)Fe(C0)4, on the basis of preliminary infrared data. Tis conclusion is no longer tenable. I t is of interest that the degeneracy of the E mode for the equatorial C-0 stretching frequencies in LFe(C0)4 in solution has been lifted for the noncyclic ligand complex [(CH&N]zP(F)Fe(C0)4; when spectra were run on dry solid samples of both complexes (cyclic and noncyclic), the degeneracy of the E mode was lifted in both cases. Detailed spectral characteristics will be considered elsewhere. Addition of PF5 to the complex results in removal of the fluoride ion from the axial amidofluorophosphine ligand of LFe(C0)4 and generation of a compound with a cationic group in the axial position. The infrared data in the C - 0 stretching region and in the P-F stretching and bending region are shown in Table I for the neutral and cationic complexes as well as for Fe(C0)5. The similarity in spectra of the system before and after fluoride removal provides proof that the cationic ligand is still axial. From the data of Table I it is clear that the P-F stretching frequency of the parent ligand disappears when PF5
is added and that frequencies for the [PF6]- ion appear. Fluoride transfer to PF5 is unambiguously indicated. As expected, introduction of a positively charged ligand into a metal carbonyl brings about a sharp increase \ i n C-0 stretching frequencies. This fact is attributable to a reduction in Fe-C back-bonding. More detailed analysis of frequency shifts will be presented in the full paper. The reduction in Fe-C backbonding suggests that weakening of the metal-carbon bond has occurred. Preliminary data support this premise which is being tested further. It is of obvious interest and significance. The N M R data on the parent amidofluorophosphine iron carbonyls and on the cationic carbonyls derived from them are displayed in Table 11. Conclusions based on the I R data are reinforced by the N M R results. In the 19F spectrum the douChart I
(CH3)IbCH2CH2N(CH3)bF cyclic ligand I
(CH~)NCH~CHZN(CH~)P(F)F~(CO)~ parent carbonyl complex with cyclic ligand, 3
[(CH3)&CH2CH2N(CH,)P]+ free cyclic cation, 1
'
[ (CH3)NCH2CH2N(CH3)PFe(C0)4]+
complex carbonyl cation with cyclic ligand, 2
2233
Communications to the Editor blet attributable in both cyclic and noncyclic cases to the F bound to the phosphorus of the ligand disappears and the doublet characteristic of [PF6]- appears clearly a t low temperature. The low temperature 31Pspectrum also shows the septet characteristic of [PF6]-. The 31Pchemical shift values further show a significant trend in the series shown in Chart I. The 31Pa values relative to H3P04 are - 138, - 182, -264, and -294 ppm, respectively. Comparable values for the noncyclic ligand series are -153, -192, -264, and -308 ppm. Increasingly negative values indicate that the phosphorus is becoming more deshielded, and more acidic through each series. In all cases this increased acidity shows up as more facile exchange of fluoride between the PF6- ion and the phosphorus of the cation. For cation 2 and [PFs]- the fluoride doublet of [PF6]- collapses at about -60 OC, indicating rapid exchange of fluoride between [PF6]- and cation 2. In contrast the 19F doublet of the [PF6]- associated with the simple, noncoordinated cyclic cation 1 shows no collapse up to above 60 OC. Corresponding temperatures for the noncyclic case are -72 and 10 OC. In studying this phenomenon of fluoride lability, purity of the system is extremely important. Small traces of base have dramatic effects in raising collapse temperature~.~ Amidofluorophosphine metal carbonyls involving Ni, Pt, P, Cr, W, Mn, Co, Cu, and Ag, have been Most react with PFs to generate [PF6]- and the corresponding cationic carbonyl complex.
0
t
-
0
A
In hv 7
A
-
CH2CI CHCl3
do
A 0
6
0
0
0
A
.
I 3
4
I/rxio' ( * K - ' )
5
Figure 1. Logarithmic plot o f aluminum-27 line widths, Av, for the 1 : l acetyl chloride-aluminum chloride complex and solvent viscosities,'5 q , vs. reciprocal temperature. Concentrations are 1.4 M for methylene chloride. 0.1 18 M for chloroform.
Acknowledgment. The support of the National Science Foundation through Grant G P 32079 is gratefully acknowledged. ,oo+
O0
References and Notes (1) S. Fleming, M. K. Lupton, and K. Jekot, Inorg. Chem., 11 2534 (1972). (2) M. G. Thomas, C. W. Schultz, and R. W. Parry, Inorg. Chem., 16, 994 (1977). (3) The noncyclic complex [(CzH&N)] pP(F)Fe(CO)* was described by Douglas and Ruff: W. M. Douglas and J. K. Ruff, J. Chem. SOC.A, 3558 (1971). Members of this general family served as starting materials for this work. (4) D. W. Bennett, R. Neustadt, R. W. Parry, and F. W. Cagle, unpublished work. (5) B. T. Kilbourn, V. A. Raeburn, and 0. T. Thompson, J. Chem. SOC.A, 1906 (1969). (6)D. J. Darensbourg, H. H. Nelson, and C. L. Hyde, Inorg. Chem., 13, 2135 (1974). (7) Detailed paper from this laboratory to be published later. (8) The iron carbonyl complex was characterized b elemental analysis, mass spectroscopy, melting point, and NMR for 31P, F, and 'H, UV, and Infrared spectra. Others have been characterized by combinations of these techniques.
'J
R. G . Montemayor, Dennis T. Sauer, Sr. Suzanne Fleming, Dennis W. Bennett, Michael G . Thomas, Robert W. Parry* Department of Chemistry, University of Utah Salt Lake City, Utah 841 12 Received October 21, 1977
.S
;
I C H,COCl~AICl,]
Figure 2. Aluminum-27 line widths, Av, for the 1:l acetyl chloride-aluminum chloride complex i n methylene chloride vs. concentration. Temperature i s 28 'C.
lH N M R spectrum.6a The 27A1N M R spectrum of this 1:l complex has not been reported to our knowledge, although the 27AlN M R parameters for aluminum chloride in acetyl chloride have been interpreted7 to favor an ion-pair structure. The 27Al and 'H N M R results reported here demonstrate that the 1:l complex between acetyl chloride and aluminum chloride has a donor-acceptor structure in methylene chloride solution; only a minor fraction, if any at all, is present as the ion-pair form. Our conclusions come from two aspects of this A Donor-Acceptor Structure for the Acetyl Chloridestudy: the temperature and concentration dependence of the Aluminum Chloride Complex in Methylene Chloride 27A1N M R spectra of the 1:l complex; the products shown by from Aluminum-27 Nuclear Magnetic Resonance 27Aland 'H N M R to be formed on addition of halide ion to Sir: acetyl chloride-aluminum chloride and to acetyl bromideAlthough the Friedel-Crafts reaction is a familiar ~ n e , l - ~ aluminum chloride complexes. 27AlFT N M R spectra (at 15.636 MHz) of the 1:l complex8 the structure of the 1:l complex between acetyl chloride and showed the following features: the line width, greater than that aluminum chloride in solvents relevant to usual synthetic of tetrachloroaluminate by at least two orders of magnitude, practice is not well defined. An ion-pair structure for the solid showed a slight temperature and concentration dependence was determined by x-ray diffraction4 after many conflicting (Figure 1, 2); the chemical shift, 92.4 ~ p m did , ~ not change solid-state IR studies had been r e p ~ r t e d .The ~ ? ~'H, 19F, and over a temperature range of -60 to 40 *C and over a concen13CN M R studies of Olah and coworkers6 on acetyl halides and tration range of to 2 M . The large line width and the Lewis acids indicate that either the ion-pair or donor-acceptor chemical shift show that the complex does not exist as sepaform may be present, depending on the solvent system. The rated ion pairs in methylene chloride.1° The temperature dedonor-acceptor form is indicated for the 1:1 acetyl chloridependence of the line width can be accounted for by visaluminum chloride complex in 1,2-dichloroethane from the @ 1978 American Chemical Society 0002-7863/78/1500-2233$01 .OO/O
