Secondary phosphine oxides SPOs

The simplest supramolecular bidentate ligand derives from secondary phosphine oxides (SPO). Complexes of transition metals with SPOs have been known for 45 years, and they were introduced as catalysts by van Leeuwen and Roobeek in the early 1980s (66). The complex used first was a platinum hydride containing two SPOs, cormected to one another by a strong hydrogen bond, and a triphenylphosphine to complete the coordination sphere. SPOs have a very strong tendency to occur in pairs connected by hydrogen bonds in many metal complexes they act as bidentate monoanions. 

The secondary phosphine oxide shown in entries 7 and 8 is the most important representative of the family of F-stereogenic secondary phosphine oxides (SPOs), which can be used directly as P-donor ligands to transition metals. Furthermore, this particular compound has been also used to prepare many mono- and diphosphine oxides by stereoselective alkylation and other reactions. ... 

Replacement of one C-substituent in phosphines by an alkoxy or aryloxy group produces esters of phosphinous acid (phosphinites). Further substitution of alkyl or aryl by oxy groups gives first the diesters of phosphonous acid (phosphonites) and finally triesters of phosphorous acid (phosphites). Secondary phosphine oxides (SPOs) or heteroatom-substituted phosphine oxides (HASPOs), which are derived from the corresponding free acids by tautomerism, have been only occasionally investigated as ligands. However, they play a pivotal role as hydrolysis products of esters. In this role, they may exert an impact on the catalytic reaction. 

Buono and Giordano focused their research on secondary phosphine oxides (SPOs), which are interesting pre-ligands for transition metals. They confer... 

Fig. 15 Secondary phosphine oxide (SPO) used as stabilizers for the RuNPs left) and TEM images of RuNPs and partiele size disbihutirai obtained with ligand LI. (Adapted from [102] with permission from RSQ...

An alternative approach to ensure selective monoarylations of ketimines, including those without meta-substituents, was based on the development of a novel catalytic system. Significant progress was achieved with air-stable (heteroatom-substituted) secondary phosphine oxides (HA)SPOs, since these preligands gave rise to arylation reactions also with less reactive, yet inexpensive, aryl chlorides as electrophiles. Here, the sterically hindered derivative (l-Ad)2P(0)H (54) was found... 

SPO = secondary phosphine oxide HASPO = heteroatom substituted phosphine oxide... 

Figure 3.7 (Left) TEM images of Ru NPs and particle size distribution obtained with secondary phosphine oxide ligand LI (right) other SPOs used as stabilizers for Ru NPs. Adapted from Ref [57]...

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