Tungsten Carbonyl Complexes Containing Positively Charged Phosphorus Ligands

Two positively charged complexes, (CO)5WP(C6H5)2CH2CH2-+P(C6H5)2(CH2C6H5) Br- and (CO)5W(C6H5)2PCH2+P(C6H5)2CH3 I-, were synthesized, and their carbonyl stretching frequencies and force constants were compared to those of the uncharged complexes, (CO)5WP(C6H5)2CH2CH2P(C6H5)2 and (CO)5WP(C6H5)2-CH2P(C6H5)2. Within experimental error, no differences in infrared data were noted for (CO)5WP(C6H5)2CH2CH2+P(C6H5)2-(CH2C6H5) Br- and (CO)5WP(C6H5)2CH2CH2P(C6H5)2. The complex (CO)5WP(C6H5)2CH2+P(C6H5)2CH3 I- had a significantly larger k1 force constant than did (CO)5WP(C6H5)2CH2P(C6H5)2. This effect is interpreted as arising from the ability of the positive charge to withdraw electron density from the metal which weakens the metal-carbon bond and strengthens the C O bond. A tungsten-phosphorus coupling constant of 270 Hz was recorded for (CO)5W(C6H5)2PCH2CH2P(C6H5)2 which suggests a metal-phosphorus bond of the same strength as the metal-phosphorus bond in (CO)5WP(C6H5)3. A phosphorus-phosphorus coupling value of 32.1 Hz was noted. Synthetically, it was observed that C6H5NH2W(CO)5 reacts with (C6H5)2PCH2CH2P(C6H5)2 to give a mixture of (CO)5WP(C6H5)2-CH2CH2P(C6H5)2 and (CO)5W(C6H5)2PCH2CH2P(C6H5)2(W(CO)5) with the formation of the latter being favored. The monometallic product can be obtained predominantly if a large excess of free ligand is employed in the reaction. With (C6H5)2PCH2P(C6H5)2, there is no tendency for the formation of the dimetallic complex nor does the monometallic complex (CO)5W(C6H5)2CH2P(C6H5)2 react with benzyl bromide. The inactivity of the dangling phosphorus is thought to be steric in nature because quaternization does occur with iodomethane. Attempts to prepare a complex such as (CO)5WP(C6H5)2+N(C2H5)3 BF-4 with the positive charge in the position alpha to phosphorus were unsuccessful. Infrared evidence is presented which suggests that the reaction between (C6H5)2PCH2CH+P(C6H5)2CH2C6H5Br- and C6H5NH2W(CO)5 in methanol yields predominantly (CO)4Br-WP(C6H5)2CH2-CH2+P(C6H5)2CH2C6H5 which represents a new class of compounds