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Infrared Studies of Group Vib Metal Carbonyl Derivatives

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Infrared Studies of Group Vib Metal Carbonyl Derivatives INFRARED STUDIES OF GROUP VIB METAL CARBONYL DERIVATIVES APPROVED t Graduate CommitteeJ irmci Maj6r Prenfessor Committee Member ciu.// Committee Member mmittee Member Director of the Department of Chemistry Dean df the Graduate School Brown, Richard A.. Infrared Studies of Group VIB Metal Carbonvl Derivatives. Doctor of Philosophy (Chemistry), August, 1971, 80 pp., 17 tables, 17 figures, bibliography, 66 titles. The infrared spectra in the carbonyl stretching region and metal-carbon stretching region have been obtained for sixty-one derivatives of M(C0)g (M * Cr, Mo, or W). The CO and MC stretch- ing frequencies have been used to help resolve the inconsistencies and discrepancies on bonding in octahedral metal carbonyls found in the literature. Thirty-seven monosubstituted complexes of the general formula LM(C0)5 (L SS a monodentate ligand containing a N, P, As, Sb, Bi, 0, or S donor atom) were prepared by thermal, photolytic, or re- placement reactions in various organic solvents. Twenty-six di- substituted complexes of the general formula cls-(bid)M(CO)^ (bid = a bidentate ligand containing N, P, As, or S donor atoms) were also prepared. Plots of the A^ and E mode carbonyl stretching frequencies and the k^ and CO force constants of ten (amine)W(C0)^ com- plexes vs. the pK of the amine were made. No correlations be- tween the trans -CO parameters [t>(C0) A^ and k^] and the pK& could be identified. Consequently, it was concluded that the isotropic inductive effect, which transmits electronic charge through the central metal sigma system, has no observable effect on the CO stretching frequencies. Very good linear trends were obtained from plots of the pK& of the ligand vs. the cis-CO parameters (2) £*(C0) Ax , i>(C0) E, and 1^3• These trends can be explained by a "direct ligand to ligand donation" first proposed by Fenske in 1970 for the Mn(CO)^X series. In this through space donation, the ligand sigma orbital overlaps with the pi system of the equa- torial MCO groups. An increase in the basicity of the ligand produces a greater overlap and this is exhibited' by a lower CO stretching frequency. The following order of importance as ligand bonding properties affect the CO stretching frequencies is con- cluded! pi bonding) through space bonding^ sigma bonding. The use of CO stretching frequencies to predict the MC bond- ing properties has been necessary in the past because of the lack of MC stretching frequencies in the literature, In this investi- gation, plots of the MC E mode stretching frequency were made against the CO E mode stretching frequency, pK& of the ligand, and Pauling electronegativity of the ligand donor atom. The plot of the CO vs. the MC stretching frequencies shows two trends. First, a distinct decrease in CO stretching fre- quency is accompanied by a decrease in the MC stretching fre- quency when complexes containing different ligand donor atoms are compared. Second, within a series of complexes which contain pi-bonding ligands with the same donor atom, the expected inverse relationship is seen. An accurate inverse relationship is found between the MC stretching frequency and the Pauling electronegativity of the donor atom. This trend supports the ligand to ligand donation concept. It has been found that the MC stretching frequency for complexes which contain ligands with aliphatic substituents can be determined within ±1.2 cm"1 by the following equation! V(MC) « -20,6 [electronegativity of the donor atom] + 431. From the evidence obtained in this investigation, the fol- lowing order of importance for ligand bonding effects on the MC stretching frequency is obtained! through space donation) pi bonding) sigma bonding. It is concluded that variations in MC frequencies in octa- hedral metal carbonyl complexes brought about by differences in the ligand bonding properties are dependent on the above three factors, whereas CO frequencies are affected only by through space and pi-bonding effects. • MP INFRARED STUDIES OF GROUP VIB METAL CARBONYL DERIVATIVES DISSERTATION Presented to the Graduate Council of the North Texas State University in Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY By Richard it. Brown, B, A,f M. S. T, A H Denton, Texas August, 1971 TABLE OF CONTENTS Page LIST OF TABLES iv LIST OF ILLUSTRATIONS . vt LIST OF ABBREVIATIONS AND SYMBOLS . .viii Chapter I. INTRODUCTION 1 Bonding Theories The Problem II. EXPERIMENTAL PROCEDURES 17 Reagents and Supplementary Techniques Preparations Infrared Spectra Elemental Analyses III. INFRARED STUDIES OF MONOSUBSTITUTED DERIVATIVES . 27 Carbonyl Stretching Region Metal-Carbon Stretching Region Unmeasurable Factors IV. INFRARED STUDIES OF DISUBSTITUTED DERIVATIVES . 61 V. SUMMARY. 69 General Conclusions Proposals for Future Work APPENDIX. BIBLIOGRAPHY ....... 77 iii LIST OF TABLES Table Page I, Force Constants for Molybdenum Carbonyls 8 Hi, CO Stretching Frequencies and Force Constants in LMo(CO)^ Molecules 9 III. Effect of Charge on y(CO) and i>(MC), in cm of Some Isoelectronic Metal Carbonyls. 10 IV. Metal-carbon and Carbon-oxygen Stretching Frequencies for Some cis-^MoCCO)^ Molecules. , . ....... 15 V. Analyses and Physical Data for Monosubstituted Metal Carbonyl Derivatives . 24 VI. Analyses for Monosubstituted and Disubstituted Octahedral Metal Carbonyl Derivatives. ... 25 VII. Solvent Effects on LW(CO)^ Complexes, in cm"1 . 28 VIII. Carbonyl Stretching Frequencies for Group VIB Monosubstituted Products ... 39 IX. Far Infrared Spectra of Monosubstituted Products of the Group VIB Metal Carbonyls 49 X. Band Ranges of Donor Atom Complexes . 51 XI. Effect on i>(CO) and i>(MC) for a Decreasing Ligand Bonding Effect. ........... 57 XII. Carbonjrl Stretching Frequencies For cis-disub- stituted Group VIB Metal Carbonyl Deriva- tives in Carbon Disulfide Solutions 62 XIII. Far Infrared Frequencies for cis-disubstituted Group VIB Metal Carbonyl Derivatives in Methylene Chloride Solutions ... 63 XIV. MC Vibrations of cis-MoCCO)^!^ Complexes, .... 65 XV. Intense Metal-carbon Stretching Frequencies of cis-disubstituted Tungsten Carbonyls .... 67 iv LIST OF TABLES Continued Table Page XVI. Metal-carbon Stretching Frequencies for trans-disubstituted Complexes. 68 XVII, Ligands for Future Complexes. 71 LIST OF ILLUSTRATIONS Figure Page 1. Resonance Structures of Nickel Carbonyl. «... 2 2. Far Infrared Spectrum of the Diars Ligand, ... 30 3. Far Infrared Spectrum of (diars)W(CO)^ ..... 31 4. Far Infrared Spectrum of (diars)Mo(CO)^. .... 32 5. Far Infrared Spectrum of (diars )Cr(CX))^. .... 33 6. Infrared Spectrum of PhoFW(CO),- in the CO Region 34 7. Far Infrared Spectrum of Ph^PWCCO)^. ...... 35 8. Infrared Spectrum of (BuO)oFW(CO)c in the CO Region .•...r...«....... 36 9. Far Infrared Spectrum of (BuO)gPW(CO),j . ... .37 10. Plot of the pK vs. the A^^ 9(CO) for amineW(C07^ complexes ........... 41 11. Plot of the pK vs. the v(C0) for amineW(C07ej complexes ........... 42 12. Plot of the pK vs. the E »(C0) for amineW(CO;^ complexes . 43 13. Plot of the pK vs. the kx CO Force Constant for amineW(CO)^ complexes 45 14. Plot of the pKQ vs. the k2 CO Force Constant for amineW(CO)^ complexes.. 46 15. Plot of the E Mode g(MC) vs. the E Mode v(CO) for Tungsten Pentacarbonyl Complexes. ... 52 16. Plot of the E Mode »>(MC) vs. the Mode Carbonyl Stretching Frequency for Tungsten Pentacarbonyl Complexes .......... 54 vi LIST OF ILLUSTRATIONS Continued Figure Page 17. Plot of the E Mode tf(MC) v&. the Pauling Electronegativity for Tungsten Penta- carbonyl Complexes. 55 vii LIST OF ABBREVIATIONS AND SYMBOLS an ss aniline ba « benzylamine bid * bidentate ligand Bu » n-butyl cha = cyclohexylamine dea « diethylamine diars » o-phenylemebis(dimethylarsine) dien » diethylenetriamine diphos = bis(l,2-diphenylphosphino)ethane dmf ss diraethylf ormamide dpae » bis(1,2-diphenylarsino)ethane dth = 2,5-dithiahexane dto ss 2,2,7,7-tetramethyl-3,6 -dithiaoctane Et ss ethyl L » monodentate ligand Me ss methyl rarph ss morpholine prop ss n-propanol o-Clan ss o-chloroaniline p-anis ss p-anisidine p-Clan ss p-chloroaniline P-en ss ethylenediphosphine viii LIST OF ABBREVIATIONS AND SYMBOLS Continued Ph » phenyl phen as o-phenanthroline 4-pic ss 4-picoline pipd = piperidine ptpz » piperaztne Pver • P(OCH2)3CCH3 py » pyridine thf = tetrahydrofuran tht « tetrahydrothiophene traen as tetramethylethylenediamine tmpa = tetramethylpropylenediamine X = CI, Br, I O - phosphorus complexes • a= amine complexes V •« acetonitrile complex V = oxygen complexes A as antimony complexes A as sulfur complexes • as arsenic complexes • « bismuth complexes ix CHAPTER I INTRODUCTION Bonding Theories Since this thesis is related to the controversial sub- ject of bonding in metal carbonyls, it is fitting to begin with a discussion of the various bonding theories that have been presented. In 1935 Brockway and Cross (1) published the unexpected result that the nickel-carbon bond length in Ni(CO)^ was ab- normally short in relation to the predicted bond length de- termined from the individual covalent radii. This was in- terpreted as evidence of multiple bonding between the metal and carbon atoms, and was explained by a series of Pauling valence bond resonance structures involving double bonds, as shown in Figure 1, This idea was further explained in Pauling's monograph (2), Since that time, it has become evident that metal car- bonyls are a very special class of compounds. They may be thought of as formed from the carbon monoxide molecule and a zero-valent transition metal atom. First, the metals obey the effective atomic number rule by attaining an elec- tronic configuration which is the same as the next rare gas. Second, compounds which contain a central metal atom in a III C C I •U=V; :C=0- :6=C=Ni=C=6i I C B. 13! C. C Osc-Ni — CSQ: A. 0: II II c C 11 II :0—c Ni= :C=0: :0=C* -MI' :C==0; I I! C C D.
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