A complex comprising a ligand of formula (I), wherein each R1, which may be the same or different, is hydrogen, an optionally substituted C1-20 hydrocarbyl group, N(R5)2, silyl, siloxy; an optionally substituted heteroaryl group, an optionally substituted heterocyclyl group or two R1 groups on adjacent carbon atoms taken together may form an optionally substituted 5- to 8-membered fused ring; each R2, which may be the same or different is hydrogen, is hydrogen, an optionally substituted C1-20 hydrocarbyl group, N(R5)2, silyl, siloxy; an optionally substituted heteroaryl group, or an optionally substituted heterocyclyl group; R3, which binds to the 6-membered ring of the indenyl group, is —(Si(R5)2)p—, where p is 1 or 2, —(C(R5)2)n- where n is an integer of 2 or more; each R4 which may be the same or different, is hydrogen, an optionally substituted C1-20 hydrocarbyl group, N(R5)2, silyl, siloxy, an optionally substituted heteroaryl group, an optionally substituted heterocyclyl group or two R4 groups on adjacent carbon atoms taken together can form an optionally substituted 5- to 8-membered fused carbon ring; each R5, which may be the same or different, is hydrogen, an optionally substituted C1-20 hydrocarbyl group, or two R5 groups taken together can form an optionally substituted 5- to 8-membered ring; a is 0 to 3; b is 0 to 3; c is 0 to 4; complexed to a metal ion, M.