Martin N. Ackermann

Tetracarbonylmolybdenum complexes of 2-(phenylazo)pyridine ligands. Correlations of molybdenum-95 chemical shifts with electronic, infrared, and electrochemical properties

Abstract The complexes cis -Mo(CO) 4 (X-2-(phenylazo)pyridine) (X = 4-CH 3 O, 4-CH 3 , 4-Cl, 5-Br, 5-CF 3 , {6-CH 3 } and cis -Mo(CO) 4 (2-(2-CH 3 -phenylazo)pyridine) have been synthesized and characterized by cyclic voltammetry, by visible and infrared spectroscopy, and by 1 H, 13 C, and 95 Mo NMR spectroscopy. The 95 Mo chemical shift correlates with the lowest energy electronic transition, with the sum of the carbonyl stretching frequencies, with the first oxidation potential, and with Hammett σ parameters for the pyridyl substituents. The failure of the complexes cis -Mo(CO) 4 (6-CH 3 -2-(phenylazo)pyridine) and cis -Mo(CO) 4 (2-(2-CH 3 -phenylazo)pyridine) to fit some of the correlations is attributed to steric or electronic effects. The effect of a substituent on the pyridyl ring of 2-(phenylazo)pyridine appears to be entirely an inductive one operating through the σ bonding. It is suggested that the 2-(phenylazo)pyridines might be appropriately viewed as ligands whose strong π-acceptor ability resides with the azo group, while the pyridyl group acts primarily as a pyridine whose basicity has been decreased by the strong electron-withdrawing 2-phenylazo substituent.

Synthesis and studies of cis-Mo(CO)2(L–L′)2 and Mo(L–L′)3 complexes of 2-(phenylazo)pyridines (L–L′) and the crystal structures of Mo(CO)2(4-methyl-2-(phenylazo)pyridine)2 and Mo(4-methyl-2-(phenylazo)pyridine)3

Abstract The complexes cis -Mo(CO) 2 (X-2-(phenylazo)pyridine) 2 ( III ) and Mo(X-2-(phenylazo)pyridine) 3 ( IV ) (X=4-CH 3 O ( a ), 4-CH 3 ( b ), H ( c ), 4-Cl ( d ), 5-Br ( e ), 5-CF 3 ( f ), 6-CH 3 ( g )), cis -Mo(CO) 2 (2-(2-CH 3 -phenylazo)pyridine) 2 ( IIIh ), and Mo(2-(2-CH 3 -phenylazo)pyridine) 3 ( IVh ) have been synthesized and characterized by cyclic voltammetry, by visible and infrared spectroscopy, and by 1 H, 13 C, and 95 Mo NMR spectroscopy. Correlations among these data and correlations of the data with the Hammett σ parameter within each series of complexes were investigated. Initially, correlations were found only for the Hammett σ parameter with the first oxidation potential and with the first reduction potential for both the type III and type IV complexes and with the sum of the carbonyl stretching frequencies for the type III complexes. However, combining 95 Mo NMR linewidth and chemical shift data for this quadrupolar metal allowed separation of the nephelauxetic and spectrochemical effects and revealed a number of additional correlations. The X-ray crystal structures of cis -Mo(CO) 2 (4-CH 3 -2-(phenylazo)pyridine) 2 ( IIIb ) and Mo(4-CH 3 -2-(phenylazo)pyridine) 3 ( IVb ) also have been determined. In IIIb each CO is trans to a pyridyl nitrogen of a 2-(phenylazo)pyridine ligand. In IVb each pyridyl nitrogen is trans to an azo nitrogen, yielding the facial isomer of the complex.

Infrared spectra and vibrational assignments of trans–CH3N–NH, CH3N–ND, CD3N–NH, and CD3N–ND

Based on infrared spectra (4000–200 cm−1) of the gas phase, condensed phase (77°K), and nitrogen matrices (20°K) vibrational assignments for trans‐CH3N–NH, CH3N–ND,  CD3N–NH, and CD3N–ND have been obtained. The assignments of the fifteen fundamentals of each molecule are well founded in experiment except for the provisional values for the torsional mode. For trans‐CH3N–NH the fundamentals are: (a′) 3127, 2992, 2925, 1559, 1457, 1435, 1382, 1120, 920, and 557 cm−1, (a″) 2988, 1430, 1140, 844, and ∼ 170 cm−1. Normal coordinate calculations are presented in support of these assignments and as a basis for further analysis of the published infrared spectra of the parent molecule, trans‐N2H2. It is shown that the spectra for N2H2, N2HD, and N2D2 can now be interpreted in a unified way.

Synthesis and characterization of cis-Mo(CO)4(L-L') and cis-Mo(CO)2(L-L')2 complexes of N(1)-methyl-2-(arylazo)imidazoles (L-L'). Correlations of spectroscopic data with substituent effects

Abstract N(1)-Methyl-2-(p-X-phenylazo)imidazoles (L–L′; X=CH3O, CH3, H, Br, CF3, NO2) react with cis-(norbornadiene)Mo(CO)4 and Mo(CO)3(CH3CN)3 to provide the complexes cis-Mo(CO)4(L–L′) (X=CH3O, CH3, H, Br, CF3, NO2) and cis-Mo(CO)2(L–L′)2 (X=CH3, H, Br, CF3), respectively. The complexes were characterized by visible and infrared spectroscopy, by 1H-, 13C- and 95Mo-NMR spectroscopy, and by cyclic voltammetry. Correlations among the data and correlations of the data with the Hammett sigma parameter within each set of complexes were investigated and are generally very good. These data, as well as the inability to synthesize complexes of the type Mo(L–L′)3, indicate that 2-(arylazo)imidazoles are less effective ligands at stabilizing complexes of zerovalent metals than are 2-(arylazo)pyridines.

Tungsten pentacarbonyl complexes of cis- and trans-1,2-dimethyldiazene and 1,2-dimethylhydrazine. Preferential oxidation of the coordinated hydrazine to the cis-diazene complex.

Abstract The complexes W(CO) 5 L (L=CH 3 NHNHCH 3 , c-CH 3 N=NCH 3 , t-CH 3 N=NCH 3 ) and [W(CO) 5 ] 2 (t-CH 3 N=NCH 3 ) have been obtained from the reaction of W(CO) 5 THF with the corresponding ligand. Each W(CO) 5 group is coordinated to the lone pair of one of the nitrogen atoms of the ligand. W(CO) 5 (c-CH 3 N=NCH 3 ) undergoes coordination site exchange between the two nitrogen atoms with a coalescence temperature of 40 + 2°C and ΔG† = 16.0 + 0.1 kcal/mole in the NMR spectrum. Infrared, visible, and NMR spectra are interpreted and comparisons drawn with other Group VIB carbonyl complexes of diazenes. The role of alkyl group size in determining the types of complexes formed by cis and trans acyclic diazenes and the properties of these complexes is discussed. Activated MnO 2 was found to preferentially oxidize CH 3 NHNHCH 3 to c-CH 3 N=NCH 3 at -50°C, offering a convenient large scale synthesis of this molecule. The hydrazine complex W(CO) 5 (CH 3 NHNHCH 3 ) is similarly oxidized in high yield to about a 5:1 mixture of W(CO) 5 (c-CH 3 N=NCH 3 ) and W(CO) 5 (t-CH 3 N=NCH3 5 ) and is the better synthetic route to these complexes. W(CO) 5 (c-CH 3 N=NCH 3 ) tautomerizes readily to a complex of formaldehyde methylhydrazone W(CO) 5 (H 2 C=NNHCH 3 ), which is believed to be coordinated through the imino nitrogen.

Tetracarbonylmolybdenum complexes of 2-(phenylhydrazino)pyridine ligands.: Correlations of spectroscopic data with pyridyl substituent effects

Abstract The 2-(phenylhydrazino)pyridine (2-PHP) complexes cis -Mo(CO) 4 (X2-(phenylhydrazino)pyridine) (X=4-CH 3 O, 4-CH 3 , H, 4-Cl, 5-Br, 6-CH 3 , 4,6-(CH 3 ) 2 ) and cis -Mo(CO) 4 (2-(2-CH 3 phenylhydrazino)pyridine) have been synthesized and characterized. The properties of these complexes are compared with those of the analogous 2-(phenylazo)pyridine (2-PAP) complexes. The lack of the π-accepting azo group in the 2-PHP ligands leads to less stable complexes, including the inability even to isolate the complex with X=CF 3 . The 2-PHP complexes show very good correlations among the 95 Mo-NMR chemical shift, the sum of the carbonyl stretching frequencies, and the Hammett σ parameter for the pyridyl substituents. There is also an excellent correlation ( r =0.978, n =7) of the 95 Mo chemical shift of the 2-PHP complexes with the shift for the 2-PAP complexes. The failure of the complexes with X=6-CH 3 or 4,6-(CH 3 ) 2 or the complex cis -Mo(CO) 4 (2-(2-CH 3 phenylhydrazino)pyridine) to fit some of the correlations is attributed to steric or electronic effects. The 2-hydrazinopyridine complex cis -Mo(CO) 4 (H 2 NHNC 5 H 4 N) also was characterized.

Diazene ligand geometry effects on the formation and properties of metal carbonyl complexes. Group vib pentacarbonyl complexes of cis- and trans-1,2-diisopropyldiazene and 1,2-diisopropylhydrazine

Abstract The Group VIB complexes M(CO)5L have been synthesized for the cases L= cis-1,2-diisopropyldiazene (c-DIPD) with M = Cr, Mo, W, L = trans-1,2-diisopropyldiazene (t-DIPD) with M = Or, W, and L, = 1,2-diisopropylhydrazine (DIPH) with M = Cr, W. Failure to obtain any bimetallic complexes is discussed in terms of steric interactions of these and related complexes. The significance of diazene ligand geometry is demonstrated by the differences in properties of the c-DIPD and t-DIPD complexes. The available evidence indicates that cis diazenes are better ligands than their trans isomers. Complex stability decreases in the order W > Cr > Mo and c-DIPD > t-DIPD. Infrared, visible, and NMR spectra are interpreted in terms of bonding in the complexes. A 30–60 cm−1 reduction of v(NN) of the diazenes upon coordination is attributed to metal-ligand π-bonding with c-DIPD being a better π-acceptor than t-DIPD. The NMR spectra of the c-DIPD complexes are temperature dependent and show that the M(CO)5 moiety undergoes coordination site exchange between the two nitrogen atoms. No exchange occurs in the t-DIPD complexes. Coalescence temperatures of 10, −48, and 60°C were recorded for the Cr, Mo, and W complexes of c-DIPD respectively, with the Gibbs free energy barriers of 15.0, 11.5 and 15.0 kcal/ mol. A comparison with exchange in other M(CO)5(cis-diazene) complexes is made and the role of the diazene structure on the reaction rate is discussed. The M(CO)5(DIPH) (M = Cr, W) complexes have been oxidized by H2O2/Cu2+ and by activated MnO2 to DIPD complexes in low yield. The tungsten DIPH complex gives only W(CO)5(t-DIPD) but the chromium system gives predominantly Cr(CO)5(c-DIPD).

Cyclooctatetraenehexacarbonyldimanganese, (C8H8)Mn2(CO)6. A corrected structural formulation, based on an x-ray crystallographic study

Abstract The structure of (C 8 H 8 )Mn 2 (CO) 6 has been determined by a single crystal X-ray diffraction study. The molecule may be regarded as a derivative of Mn 2 (CO) 10 in which 2 carbon monoxide ligands have been replaced by diene units from the C 8 H 8 ligand, with concomitant lengthening of the MnMn bond

Monometallic and bridged bimetallic (including mixed metal) complexes of 2,3-diazabicyclohept-2-ene with group vib tetracarbonyl moieties

Abstract Complexes of the type M(CO) 4 L 2 (L = 2,3-diazabicyclohept-2-ene; M = Cr, Mo, W) and the bridging systems (CO) 4 ML 2 M′(CO) 4 (M = M′ = Mo; M = Mo, M′ = Cr) have been prepared.

Chromium, tungsten, iron, and ruthenium complexes of the 4-membered ring diazene 3,4-diazatricyclo[4.2.1.02,5]non-3-ene

Abstract The 4-membered ring diazene 3,4-diazatricyclo[4.2.1.0 2,5 ]non-3-ene (dtn) reacts with Cr and W carbonyls to give the complexes M(CO) 5 (dtn))(Ia,b), [M(CO) 5 ] 2 (dtn) (IIa,b), M(CO) 4 (dtn) 2 (IIIa,b), [M(CO) 4 ] 2 (dtn) 2 (IVa,b), and [M(CO) 3 ] 2 (dtn) 3 (Va,b) where a = Cr and b = W. 1 H and 13 C NMR provide evidence that compounds III-V each exist in the predicted two isomeric forms and full assignment of the resonances is made for all but the Va 13 C spectrum. Fe 2 (CO) 9 reacts with dtn to give Fe(CO) 4 (dtn) (Ic) and Fe 3 (CO) 9 (dtn) (VIIIc). It is argued that steric effects from the hydrocarbon portion, notably C(9), of dtn prevents formation of the normally stable diiron complexes Fe 2 (CO) 6 (dtn) (VIc) and Fe 2 (CO) 7 (dtn) (VIIc). Ru 3 (CO) 12 and dtn react to form only Ru 3 CO) 9 (dtn) (VIIId). Variable temperature 13 C NMR studies reveal CO scramblingin VIIIc and VIIId at room temperature, which ceases at low temperature. Results for the dtn complexes are compared with results for another 4-membered ring diazene ligand as well as with results for 3−, 5−, and 6-membered ring diazenes.