Steric effects of bulky phosphines on ⁹⁵Mo NMR shieldings

Abstract

Three sets of substituted molybdenum carbonyl complexes of the type Mo(CO)~,(PY,), (n = 1-3) with a wide range of phosphorus ligands (Y = Ar, R, OR, NR,, C1, H) were synthesized and their respective 9 s~o NMR spectral data were collected, The steric effect of PY, plays an unexpectedly important role in the paramagnetic shielding term determining E(~'Mo), and is even observed in the least crowded M(CO),(PY,) complexes. It is deduced that the steric requirement reduces the commonly accepted a-ability of phosphites by weakening the M-P bonds, making 6 ( 9 5~~) positions move toward higher frequency in going from M(CO),(PY,) to fac-M(CO),(PY,),. A detailed correlation analysis in the case of phosphite ligands has shown that the free cone space to accommodate a PY, ligand may be as low as 95" in Mo(CO)~,(PY,), (n = 1-3) derivatives. The fair linearity of these correlations suggests indirectly that the a-component in phosphite bonding is relatively less important. These linear correlations of 6 ( 9 5~0 ) against the Tolman cone angle 9 provide an empirical estimation of the bulkiness of any phosphite ligand.

Synthesis and growth mechanism of monodispersed MoS2 sheets/carbon microspheres

“…It is reported that some broad bands around 2000 cm À1 indicated Mo(CO) 6Àx L x species (where L ¼ solvent, such as i-propanol). 32 For the as-prepared sample at 100 C (Fig. 7a), the broad bands around 2000 cm À1 were obviously distinguishable.…”

Comparative Study of Novel Phosphordiamidite and Phosphite Ligands Used in Alkene Hydroformylation; Synthesis, Characterization, Metalation, and Catalytic Evaluation

“…It is interesting that cis ‐[Mo(CO) 4 {κ 2 ‐ P , P ‐( L2 )}], 2a , undergoes CO elimination at ambient temperature because (1) typically [Mo(CO) 3 L 3 ] complexes are formed via a trisubstituted intermediate {[Mo(CO) 3 DMF 3 ] or [Mo(CO) 3 (NCMe) 3 ], } or (2) can be synthesized from [Mo(CO) 6 ] through photolysis. Either method requires high temperatures, and/or extended reaction times , . To the best of our knowledge the only other example of CO elimination from a group VI tetracarbonyl complex is with the multi/hetero‐donor ligand, Ph 2 P( o ‐C 6 H 4 )CH=N(CH 2 ) 2 ( o ‐C 5 H 4 N), (PNN) .…”

“…From this, the main effects of each variable ( a P and a T ) and an interaction term ( a PT ) are obtained. Mathematica was used to solve the system of equations and generate response surfaces …”

Determination of the Stereoelectronic Parameters of PF3, PCl3, PH3, and P(CH2CH2CN)3. The Quantitative Analysis of Ligand Effects (QALE)

“…In the early stages of the development of the QALE model (quantitative analysis of ligand effects), we also proposed that PCl 3 is a pure σ donor . The problem with empirical studies is that the total electron donor capacity of PZ 3 is the result of the combination of at least two electronic properties (σ donicity and π acidity) when PZ 3 is bonded to a transition metal. ,,,,,,,− No method has been found to separate these electronic effects when only the properties of transition-metal complexes are considered.…”