Dissociation of phosphine

The study of rapid, intermolecular ligand exchange between square-planar complexes trans-Ir(CO)L2X (X = C1 or Me, L - PPh3, P(p-tolyl)3, or PMePh2) by variable-temperature 31P NMR spectroscopy indicates that the reaction proceeds through dissociation of phosphine from the metal center and a subsequent associative substitution with other complexes 559,560 Ligand exchange between square-planar Ir and Pt complexes is slow. 

The dissociation of phosphine from RhClH2(PPh3)3, whilst limited at room temperature, increases at higher hydrogenation temperatures ... 

Under carbon monoxide, we obtain a very low quantum yield indeed. Thus, in this system, the photochemical fragmentation is preceded either by dissociation of phosphine or by dissociation of CO, and not by some other process. 

When subjected to shock-waves, phosphine dissociates into hydrogen and red phosphorus. The radiation thus emitted is only visible in reflection. In contrast, the shock-wave induced dissociation of phosphine diluted with argon is accompanied by emission of visible light. In this case the reaction products are hydrogen and white phosphorus... 

The flash photolysis of phosphine, according to spectroscopic results, causes the formation of two phosphorus- and two hydrogen-containing radicals, corresponding to the dissociation of phosphine as shown in Eqs. (6) and (7) >. 

Some notable examples of these rules are tris (triphenylphosphine) -halogenorhodium(I) studied by Osborn et al. (2) and hydridocarbonyl-tris(triphenylphosphine)rhodium(I) reported by O Connor et al. (3). A common feature of these two complexes is that the coordinative unsaturation is caused by dissociation of phosphines and that M-H bonds... 

B. H. Wilsden studied the energy involved in the electronic shifts during the dissociation of phosphine. 

Addition of free PPh3 to the complex leads to the formation of Pd(PPh3)4. Dissociation of the allene ligand is also observed for Pd[P(OPh)3]2-(PhCH=C=CHPh) and Pd[P(OMe)3]2(PhCH=C=CHPh), but dissociation of phosphine or phosphite ligands is not observed for any of these Pd(0) compounds. 

The presence of PMes inhibits the reaction. Mixtures of cis-RhH(CH2C(0)CH3)(PMe3)3Cl and cw-RhD(CD2C(0)CD3) (PMe3)3Cl led to only CH3C(0)CH3 and CD3C(0)CD3, showing that the elimination was intramolecular, which involved reversible dissociation of phosphine followed by an irreversible reductive elimination and reassociation of phosphine. ... 

Only the dissociation of phosphine and arsine show much less than a doubling of velocity. That is perhaps connected with the high temperature at which the observations... 

The complex is a white solid, insoluble in nonpolar solvents but soluble in polar solvents such as dichloromethane, ethanol, and even water. The solid is stable in air for fairly long periods. Very slow decomposition, probably by reaction with atmospheric water, is observed over several days. Solutions of the complex are pale yellow, smell of free trimethylphosphine toxic), and exhibit a very broad H NMR signal, indicating that reversible dissociation of phosphine and coordination of chloride takes place in solution. Treatment with Na[B(C6H5)4] in ethanol affords the tetraphenylborate salt, which shows a sharp, complex multi-... 

All complexes have shown high catalytic activity, even at room temperature (in contrast to platinum catalysts). Hydrosilylation in the presence of phosphine-rhodium complexes occurred in air, because real catalyst (active intermediate) was formed after oxygenation and/or dissociation of phosphine, as reported previously [14]. The non-phosphine complexes 1 and 4 are also very efficient catalysts for the hydrosilylation of allyl glycidyl ether. Irrespective of the starting precursor, a tetracoordinated Rh-H species, responsible for catalysis, is generated under reaction conditions, as illustrated in Scheme 3. 

The additions of aryl halides to PdL2 complexes of Q-phos derivatives were recently reported by Barrios-Landeros and Hartwig179. The addition to Phi, PhBr and PhCl takes place through distinct mechanistic pathways (Scheme 5). Iodobenzene reacts by associative displacement of a phosphine, bromobenzene reacts by rate-limiting dissociation of phosphine, and chlorobenzene reacts by reversible dissociation of phosphine, followed by oxidative addition. 

MMM [68] have also studied the reaction mechanism for RhCl(PH3)2 -f C2H4 -I- BH3 -> RhCl(PH3)2 -I- C2H5BH2 catalytic reaction without dissociation of phosphine ligands and have found that (i) the mechanism involving olefin insertion into the Rh-B bond is a few kilocalories per mole more favorable than that for insertion into Rh-H bond and (ii) in the preferable pathway, BH3 reacts with the catalyst before olefin does. Thus, for this reaction occurring without dissociation of a PH3 group the initial formation of a C-B bond is more favorable than initial formation of a C-H bond. DS [69] have studied the mechanism of this reaction with dissociation of one of PH3 ligands upon coordination of olefin and have shown that the insertion of olefin into the Rh-H bond is a few kilocalories per mole more favorable than that into the Rh-B bond. 

A proposed reaction pathway by which ammonia is formed is shown in Scheme 6. After the dissociation of phosphine, attack by another hydrazido complex (e.g., A) to form a bridged species, C, is proposed. Hydrazido complexes such as A are known to be good nucleophiles. For example, they react in acid catalyzed reactions with aldehydes and ketones to form diazoalkane complexes (e.g.. Equations 4 and... 

A nondissociative mechanism was also claimed for ci5-[(PPh3)2Pt(vinyl)-(alkynyl)]. The unusual rearrangement reaction (8) proceeds by initial dissociation of phosphine.A formal jS-methyl elimination must occur here, but the... 

The famous red spot observed on Jupiter may be due to red P. It could be formed by the dissociation of phosphine, which is known to be present in the planetary atmosphere [42,43]. Various photochemical reactions between PHj and H2 lead to red P (Section 4.4). 

The dissociation of phosphine is negligible unless it is heated to several hundred degrees. It is thermally more stable than AsHj but less so than NH3. Photodissociation also occurs (Chapter 13.4). At 0°C and atmospheric pressure, activated charcoal (1 cc) absorbs considerably less PH3 (69 cc) than NH3 (170 cc). 

Detailed kinetic studies provide evidence for the stepwise mechanism shown in Scheme 6.3. In this mechanism, dissociation of phosphine precedes oxidative addition. The dissociation of ligand provides a site for coordination of the C-H bond in the square plane prior to oxidative addition and follows the trend noted earlier in tiiis chapter for Wilkinson s catalyst that addition and elimination from three-coordinate species is often faster than addition and elimination from four-coordinate species. 

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