Lewis bases phosphine

Recently, Manners and co-workers have found another type of reaction, the inorganic process corresponding to Rh-catalysed dehydrocoupling of borane adducts, which is homogeneous or heterogeneous catalysed depending on the substrate, in particular the nature of the Lewis base, phosphine or amine respectively [15]. 

When the reduction of 51 is performed in the presence of Lewis bases, phosphine derivatives are formed. For anion radicals [Sl]" with limited lifetimes, mononuclear products such as [Co(CO)3(PR3)] and paramagnetic [Co(CO)2(RC2R)(PR 3)] result, but, if [51] is more stable, direct substitution to give binuclear species occurs (727, 722). 

From analogy with the cyanosilylation of aldehydes a working model for the catalytic cycle has been proposed in which the Lewis acid (Al) and the Lewis base (phosphine oxide) activate the imine and TMSCN respectively. 

It is also possible to obtain pentamers and higher oligomers as well as polymers. The addition of Lewis bases (phosphines, etc.) to the catalyst or application of complexes containing such ligands, such as [Ni P(OPh)3 4], causes an increase in yield of the lower oligomers at the expense of the higher oligomers. 

Shibasaki and coworkers developed a bifunctional chiral catalyst possessing the Lewis acid (aluminum metal) and the Lewis base (phosphine oxide), which was successfully applied to asymmetric Reissert-type reaction of trimethylsilylcyanide (TMSCN) [45]. The reaction of quinoline (92) with TMSCN and 2-furoyl chloride in the presence of Lewis acid Lewis base catalyst (91) occurred to give the Reisser product in 91% yield and 85% ee. The chiral catalyst was connected to JandaJRL... 

Towards a simple Lewis base, for example the proton, phosphine is a poorer electron donor than ammonia, the larger phosphorus atom being less able to form a stable covalent bond with the acceptor atom or molecule. Phosphine is, therefore, a much weaker base than ammonia and there is no series of phosphonium salts corresponding to the ammonium salts but phosphonium halides. PH4X (X = Cl, Br, I) can be prepared by the direct combination of phosphine with the appropriate hydrogen halide. These compounds are much more easily dissociated than ammonium halides, the most stable being the iodide, but even this dissociates at 333 K PH4I = PH3 -t- HI... 

R Tl compounds react readily with acids, halocarbons, or sulfur dioxide to form R2TIX. They also form neutral complexes (R3TI L) with Lewis bases (L), eg, amines and phosphines, in a similar manner as the gaHium and indium analogues. 

Another way of replacing chloride trans to phosphine involves using silver salts reaction with AgPF6 and AgN03 introduces, respectively, a water molecule (XII) and a nitrate group (IX), which may in turn be replaced by a range of Lewis bases, giving (VIII), (X) and (XXV). 

Trialkyls are only known as Lewis base adducts. Reaction of Au2Br6 with methyllithium at 70°C affords an unstable AuMe3 (which is probably AuMe3Br ), but stable phosphine adducts AuMe3PR3 (R, e.g. Me, Ph) can be made [169]. 

The reaction between a Lewis acid R3M and a Lewis base ER3, usually resulting in the formation of a Lewis acid-base adduct R3M—ER3, is of fundamental interest in main group chemistry. Numerous experiments, in particular reactions of alane and gallane MH3 with amines and phosphines ER3, have been performed [14]. Several general coordination modes, as summarized in Fig. 2, have been identified by X-ray diffraction. 

The literature3 contains some limited work on decaborane-based polymer systems. Typically, most utilize the Lewis acid/base reaction between decaborane (Lewis acid, B10H12) and amines and phosphines (Lewis bases, L) resulting in the formation of complexes (see scheme 2) having the general formulas B10H12L2. For example, the... 

In the presence of added Lewis bases, sonochemical ligand substitution also occurs for Fe(C0)5, ancl act or roost metal carbonyls. Sonication of Fe(C0)5 in the presence of phosphines or phosphites produces Fe(C0)5 nLn, n=1, 2, and 3. The ratio of these products is independent of length of sonication the multiply substituted products increase with increasing initial [L] Fe(C0)i L is not sonochemically converted to Fe(C0)3L2 on the time scale of its production from Fe(C0)5. These observations are consistent with the same primary sonochemical event responsible for clusterification ... 

The lustrous black crystals of trirhenium nonabromide are not rapidly degraded on exposure to the atmosphere the crystals can be stored over desiccants for months without evidence of decomposition. The bromide dissolves fairly slowly and sparingly in ether and acetone. In methanol, the bromide gives yellow-orange solutions, but it is solvolyzed within minutes. Similarly, the bromide dissolves in water at room temperature to yield a violet solution which darkens rapidly, yielding a black precipitate, presumably the hydrated dioxide.9 Contrary to published work,10 the bromide does dissolve in ammonia with solvolysis, as is evidenced by lines attributable to ammonium bromide in x-ray diffraction data of the solid residue recovered from liquid ammonia solutions.11 Trirhenium nonabromide reacts with Lewis bases such as phosphines and amines to form a series of complexes of the type (base) 3Re3Br9.6... 

An extension of the research on silver complexes with Lewis base-functionalized mono(A-heterocyclic carbene) ligands has been made toward the better-studied and stronger coordinating phosphine systems. The reaction of a diphenylphosphine-functionalized imidazolium salt with silver oxide in dichloromethane affords a trinuclear silver carbene complex 50, as confirmed by electrospray-ionization mass spectrometry.96,97 Metathesis reaction of 50 in methanol using silver nitrate gives 51 in 33% yield. The crystal structures of 51 were found to be different when different solvents were used during crystallization (Scheme 12).97 One NO3- anion was found to be chelated to... 

Phosphine, PH3, is a pyramidal molecule that has an unshared pair of electrons on the phosphorus atom. Therefore, it can function as both a proton acceptor (Pro ns ted base) or an electron pair donor (Lewis base). For the moment, it is the ability to accept protons that will be considered. When ammonia is dissolved in water, the equilibrium... 

The structure of dimethylberyllium is similar to that of trimethylaluminum except for the fact that the beryllium compound forms chains, whereas the aluminum compound forms dimers. Dimethylberyllium has the structure shown in Figure 12.3. The bridges involve an orbital on the methyl groups overlapping an orbital (probably best regarded as sp3) on the beryllium atoms to give two-electron three-center bonds. Note, however, that the bond angle Be-C-Be is unusually small. Because beryllium is a Lewis acid, the polymeric [Be(CH3)2] is separated when a Lewis base is added and adducts form. For example, with phosphine the reaction is... 

There are numerous similarities between ammonia and phosphine, but the latter is a much weaker base (see Chapter 9). In fact, phosphonium salts are stabilized by large anions that are also the conjugates of strong acids. Accordingly, the most common phosphonium salts are the iodides, bromides, tetrafluoroborates, and so forth. Phosphine and substituted phosphines are good Lewis bases toward soft Lewis acids, and many coordination compounds of this type are known. 

However, with soft electron pair acceptors such as Pt2+, Ag+, and Ir+, phosphines are stronger Lewis bases than are NH3 and amines, so phosphines and arsines interact better with class B metals than do amines. Generally, phosphines and arsines form stable complexes with second- and third-row transition metals in low oxidation states. 

The chemistry of coordination compounds comprises an area of chemistry that spans the entire spectrum from theoretical work on bonding to the synthesis of organometallic compounds. The essential feature of coordination compounds is that they involve coordinate bonds between Lewis acids and bases. Metal atoms or ions function as the Lewis acids, and the range of Lewis bases (electron pair donors) can include almost any species that has one or more unshared pairs of electrons. Electron pair donors include neutral molecules such as H20, NH3, CO, phosphines, pyridine, N2, 02, H2, and ethyl-enediamine, (H2NCH2CH2NH2). Most anions, such as OH-, Cl-, C2042-, and 11, contain unshared pairs of electrons that can be donated to Lewis acids to form coordinate bonds. The scope of coordination chemistry is indeed very broad and interdisciplinary. 

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