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Non-coordinating anion
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<p><a href="/facts/Anion/wrbwhF3z">Anions</a> that interact weakly with <a href="/facts/Cation/wrbwhF3z">cations</a> are termed non-coordinating anions, although a more accurate term is weakly coordinating anion. Non-coordinating anions are useful in studying the reactivity of <a href="/facts/Electrophilic/1AHFg1zm">electrophilic</a> cations. They are commonly found as counterions for cationic <a href="/facts/Metal_complex/1tCyeQUm">metal complexes</a> with an <a href="/facts/18-Electron_rule/KNfG6tpM">unsaturated coordination sphere</a>. These special anions are essential components of <a href="/facts/Homogeneous_catalysis/c7wplnb2">homogeneous</a> <a href="/facts/Ziegler%25E2%2580%2593Natta_catalyst/bkDSDf9d">alkene polymerisation catalysts</a>, where the active catalyst is a coordinatively unsaturated, cationic <a href="/facts/Transition_metal/0slGWoLQ">transition metal</a> complex. For example, they are employed as counterions for the <a href="/facts/Electron_counting/1bPUvehY">14 valence electron</a> cations [(C5H5)2ZrR]+ (R = methyl or a growing polyethylene chain). Complexes derived from non-coordinating anions have been used to <a href="/facts/Catalyze/LPBS7TQC">catalyze</a> <a href="/facts/Hydrogenation/l7EzNSA7">hydrogenation</a>, <a href="/facts/Hydrosilylation/dPqlRe0t">hydrosilylation</a>, <a href="/facts/Oligomerization/v7oDY8zu">oligomerization</a>, and the <a href="/facts/Living_polymerization/wUyVN7zv">living polymerization</a> of <a href="/facts/Alkene/RtYcS6kU">alkenes</a>. The popularization of non-coordinating anions has contributed to increased understanding of <a href="/facts/Agostic_complex/4VDvImoz">agostic complexes</a> wherein hydrocarbons and hydrogen serve as ligands. Non-coordinating anions are important components of many <a href="/facts/Superacid/dg82EcNa">superacids</a>, which result from the combination of <a href="/facts/Br%25C3%25B8nsted_acid/bqxQnJoX">Brønsted acids</a> and <a href="/facts/Lewis_acid/qlLqRvg2">Lewis acids</a>. </p>