Synthesis of the Bifunctional Phosphinidene Cluster, Fe3(CO)9(μ3-PH)2, and a Systematic Study of the Reactivity of the Cluster-Bound P−H Functional Group

The synthesis and systematic study of the reaction chemistry of a bifunctional phosphinidene cluster, Fe 3 (CO) 9 (μ 3 -PH) 2 ( 3 ) is reported. Reaction chemistry at one P−H functional site is effectively communicated through the Fe 3 (CO) 9 core, and impacts on the reactivity of the second P−H site. Deprotonation of the acidic protons in 3 allows access to a lone electron pair on phosphorus. The first proton is readily removed with NEt 3 /[PPN]Cl ([PPN] + = (Ph 3 P) 2 N + ) to produce the [PPN] + salt of [Fe 3 (CO) 9 (μ 3 -PH)(μ 3 -P)] - ([ 4 ] - ). Removal of both phosphorus-bound hydrogen atoms in 3 requires the use of 2 equiv of n -BuLi, to produce Li 2 [Fe 3 (CO) 9 (μ 3 -P) 2 ] (Li 2 [ 5 ]). Quenching of Li 2 [ 5 ] with MeOH- d 4 generates [Fe 3 (CO) 9 (μ 3 -PD)(μ 3 -P)] - . The lone electron pairs on the cluster-bound phosphorus atoms undergo analogous reaction chemistry to organophosphines. Alkylation at the phosphorus site is carried out by reaction of [Et 3 NH][ 4 ] with MeOSO 2 CF 3 generating the monosubstituted cluster, Fe 3 (CO) 9 (μ 3 -PMe)(μ 3 -PH) ( 6 ) as the primary product. The cluster anions [ 4 ] - and [ 8 ] -, containing a phosphorus lone pair, are oxidized by elemental sulfur to produce the phosphine sulfide complexes, [Et 3 NH][Fe 3 (CO) 9 (μ 3 -PH)(μ 3 -P S)] ([Et 3 NH][ 10 ]) and [Et 3 NH][Fe 3 (CO) 9 (μ 3 -PMe)(μ 3 -P S)] ([Et 3 NH][ 11 ]). Treatment of [ 10 ] - with an additional equivalent of NEt 3 and S 8 yields the dianionic cluster, [Et 3 NH] 2 [Fe 3 (CO) 9 (μ 3 -P S) 2 ] ([Et 3 NH] 2 [ 12 ]). Without added base, reaction of the neutral clusters, 3 and 6, with S 8 in THF solution yield the clusters Fe 3 (CO) 9 (μ 3 -PH)(μ 3 -PSCH 2 CH 2 CH 2 CH 2 OH) ( 13 ), Fe 3 (CO) 9 (μ 3 -PSCH 2 CH 2 CH 2 CH 2 OH) 2 ( 14), and Fe 3 (CO) 9 (μ 3 -PMe)(μ 3 -PSCH 2 CH 2 CH 2 CH 2 OH) ( 15 ), with a ring-opened THF molecule appended to sulfur. Reaction of 3 with S 8 in THF solution in the presence of ClAuPPh 3 produces the gold derivative, Fe 3 (CO) 9 (μ 3 -PSAuPPh 3 ) 2 ( 17 ). Like PH groups in phosphines, the μ 3 -PH moieties in 3 react with activated alkenes to yield single- and double-insertion products, Fe 3 (CO) 9 (μ 3 -PH)(μ 3 -PCH 2 CH 2 R) (R = CN ( 18a ), CO 2 Me ( 19a )) and Fe 3 (CO) 9 (μ 3 -PCH 2 CH 2 R) 2 (R = CN ( 18b ), CO 2 Me ( 19b )). The solid-state structures of 3, 17, and 18b were determined by single-crystal X-ray diffraction.