Remarkable Differences in the Coordination Chemistry of Structurally Related 1,2,4‐Triphosphaferrocenes with Copper(I) Halides and Silver(I) Salts

The coordination behavior of 1,2,4-triphosphaferrocenes [FeCpR(η5-P3C2tBu2)] [CpR = Cp (1), Cp″′ = η5-C5H2tBu3 (3)] towards CuI halides is significantly influenced by the substitution pattern of the cyclopentadienyl ring attached to the iron atom. The reaction of the Cp derivative 1 with CuBr in a 1:1 stoichiometry leads to the dimeric complex [{FeCp(η5:η1:η1-P3C2tBu2)}{μ-CuBr(MeCN)}]2 (5b), in which two 1,2,4-triphosphaferrocenes are linked by two CuBr units. By using a 1:2 stoichiometry, the 1D polymeric compound [{FeCp(η5:η1:η1:η1-P3C2tBu2)}μ-{(CuBr)3(MeCN)2}]n (6) is formed in which the triphosphaferrocenes are bridged by (CuBr)2{CuBr(MeCN)2} units. Starting from CuI, independent of the stoichiometry, the cage compound [{FeCp(η5:η1:η1-P3C2tBu2)}3{Cu(μ-I)}3{Cu(μ3-I)}3{Cu(NCMe)}(μ6-I)](7) is formed. However, if the bulky Cp″′ derivative 3 is used already in a 1:1 stoichiometry with CuBr, a transformation of the initially five-membered 1,2,4-triphospholyl ring into a four-membered 1,2-diphosphete ligand is observed, which is linked by CuBr moieties forming the dimeric paramagnetic complex [{FeCp″′(η4:η1:η1-P2C2tBu2)}(μ-CuBr)]2 (9). Furthermore, applying a 1:2 stoichiometry between 3 and CuX (X = Br, I) the complete fragmentation of the 1,2,4-triphospholyl ring under mild conditions into a tetraphosphabutadiene ligand is observed. In the formed 1D polymeric complexes [{(FeCp″′)2(μ,η4:η1:η1-P4)}{(μ-CuX)2(MeCN)}]n [X = Br (10a), I (10b)] this ligand represents now the middle deck of the triple-decker sandwich complexes linked by four-membered [(CuX)2(CH3CN)] moieties. Moreover, the reaction of the Cp derivative 1 with the Ag salt of the weakly coordinating anion [Al{OC(CF3)3}]4– leads to the dimeric Ag(CH3CN)-bridged dicationic product [{FeCp(η5-P3C2tBu2)}Ag(MeCN)]2[Al{OC(CF3)3}4]2 (11).