Lewis block metal halides

Phosphonium halides, PH4X, are formed by treating PH3 with HX but only the iodide is stable under ambient conditions. The chloride is unstable above 243 K and the bromide decomposes at 273 K. The [PH4] ion is decomposed by water (equation 14.29). Phosphine acts as a Lewis base and a range of adducts (including those with low oxidation state rf-block metal centres) are known. Examples include H3B-PH3, C13B-PH3, Ni(PH3)4 (decomposes above 243 K) and Ni(CO)2(PH3)2. Combustion of PH3 5delds H3PO4. 

Substituents at fluorenyl positions 2 and 7 are accessible in very good yields via one- or two-step reactions. The highest activity in the polymerization of ethylene was achieved by complex 35 containing bulky terf-butyl substituents (Figure 8). Polar groups are unsuitable for good catalyst performance, e.g., methoxy or halide substituents (36,37), because the heteroatom acts as a Lewis base and blocks another metal center. 

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