Platinum complexes oxygen donors

Platinum(II) Complexes with Oxygen-donor Ligands 709... 

Entries 1-22 list exo phosphines 200 whereas entries 23-30 are endo phosphines 203 (Scheme 2.62). The number of endo phosphines prepared to date is more limited, probably due to the low stereoselectivity in their formation. Entries 1-10 include exo monophosphines with additional oxygen (entries 1-6), sulfur (entries 3, 5-8) and nitrogen (entries 9 and 10) donor atoms. Entries 11-22 contain a second phosphorus or an arsenic atom, which in some cases is also stereogenic (entries 14-16 and 19 21). The compound in entry 19 is the dimerisation of DMPP, which required the use of a platinum complex. ... 

The nitrogen in the ammonia and the oxygen in the water are the donor atoms. They are the atoms that actually donate the electrons to the Lewis acid. The coordination number is the number of donor atoms that surround the central atom. As seen above, the coordination number for Cr3+ is 6. Coordination numbers are usually 2, 4 or 6, but other values can be possible. Silver (Ag ) commonly forms complexes with a coordination number of 2 zinc (Zn2+), copper (Cu2+), nickel (Ni2+), and platinum (Pt2+) commonly form complexes with a coordination number of 4 most other central ions have a coordination number of 6. 

Deviations from the E1/2-DN curves may occur with EPD molecules which can coordinate in different ways. For instance, nitrobenzene coordinates towards SbCls via an oxygen atom of the nitro group, while towards a soft EPA cation coordination via the aromatic ring appears possible. In the latter case E1/2 values would be determined not by the donicity (97) (measured towards SbCls) but by the r-donor properties of nitrobenzene. Studies of the reduction of Ag+ at the rotating platinum electrode in various EPD solvents indicate that nitrobenzene behaves as a stronger EPD than expected on basis of its donicity 39). In fact, Ag+ forms complexes with various aromatic compounds 46). Specific EPD—EPA interactions were observed in the reduction of Cu+, Ag+... 

A catalyst used in industry is very rarely a pure element or compound. Most catalysts contain a complex mixture of chemical additives or modifiers that are essential ingredients for high activity and selectivity. Promoters are beneficial additives that increase activity, selectivity, or useful catalyst lifetime (stability). Structural promoters inhibit sintering of the active catalyst phase or present compound formation between the active component and the support. The most frequently used chemical promoters are electron donors such as the alkali metals or electron acceptors such as oxygen and chlorine. For example, in the petroleum industry, chlorine and oxygen are often added to commercial platinum catalysts used for reforming reactions by which aliphatic straight-chain hydrocarbons are converted to aromatic molecules (dehydrocyclization) and branched isomers (isomerization). 

The hard-soft acid-base (HSAB) principle states that hard acids prefer to associate with, and react readily with, hard bases while soft acids prefer to associate with, and react readily with, soft bases. The HSAB principle embodies both kinetic and thermodynamic meaning. Thus, interaction between a Lewis acid and a Lewis base of comparable hardness or softness is predicted to proceed readily and result in the formation of a thermodynamically stable product. Applications of the HSAB principle to coordination chemistry abound.29 For example, DMSO is an ambidentate ligand with both hard (oxygen) and soft (sulfur) donor sites. When complexes are formed with platinum(II), a soft acid, DMSO will typically coordinate via sulfur, while, with the harder acid nickel(II), coordination via oxygen is favored. O... 

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