Reactivity of Silyl-Substituted Heterobimetallic Iron-Platinum Hydride Complexes towards Unsaturated Molecules, I Alkyne Insertions into the Platinum-Hydride Bond, Phosphane-Induced σ-Alkenyl-μ-Vinylidene Rearrangements and Formation of μ-Isonitri

摘要

The heterobimetallic hydride complexes [(OC)_3 Fe{Si(OMe)_3}(μ-Ph_2PXPPh_2)Pt(H)(PR_3)](1a: X = CH_2, PR_3 = PPh_3; 1b: X = NH, PR_3 = PPh_3; 1c: X = CH_2, PR_3 = PMePh_2) have been prepared by the oxidative addition of [(OC)_3Fe(H){Si(OMe)_3}(η~1-Ph_2PXPPh_2)] to [Pt(H_2C=CH_2)(PPh_3)_2] or by reaction of K[(OC)_3Fe{Si(OMe)_3}(η~1-dppm)] with trans-[Pt(Cl)(H)(PPh_3)_2]. The solid-state structure of compound 1b has been determined by single-crystal X-ray diffraction. 1-Alkynes such as methylpropiolate or phenylacetylene insert in a regiospecific manner into the Pt-H bond of 1 to yield the σ-alkenyl complexes [(OC)_3Fe{μ-Si(OMe)_2(OMe)}(μ-Ph_2PXPPh_2)Pt{C(R)=CH_2}] (2a: X = CH_2, R = CO_2Me; 2b: X = NH, R = CO_2Me; 3a: X = CH_2, R = Ph). Addition of the Pt-H bond of 3a across the triple bond of [D_1] phenylacetylene affords [(OC)_3Fe{μ-Si(OMe)_2(OMe)}(μ-dppm)Pt{C(Ph)=C(D)H}] (3a~*) having the deuteron trans to platinum (cis addition). This insertion reaction is accompanied by dissociation of the platinum-bonded PR_3 ligand and saturation of the vacant coordination site by a dative μ-η~2-Si-O→Pt interaction. When 3 is treated with PR_3 again, a subsequent phosphane-induced rearrangement leading to vinylidene-bridged complexes [(OC)_3Fe{μ-C=C(H)R'}(μ-Ph_2PXPPh_2)Pt(PR_3)] (4a: X = CH_2, R' = Ph, PR_3 = PPh_3; 4b: X = NH, R' = Ph, PR_3 = PPh_3; 4c: X = CH_2, R' = Ph, PR_3 = PMePh_2; 4d: X = CH_2, R' = p-tolyl, PR_3 = PPh_3) occurs. Upon purging a solution of 3a with carbon monoxide, the labile CO adduct [(OC)_3Fe{Si(OMe)_3}(μ-dppm)Pt(CO){C(Ph)=CH_2}] 5a is formed, addition of 2,6-xylyl isocyanide to 2a and 3a affords the isonitrile adducts [(OC)_3Fe{Si(OMe)_3}(μ-dppm)Pt(CNxylyl){C(R)=CH_2}] (5b: R = CO_2Me; 5c: R = Ph), respectively. When hydride complex 1a is allowed to react with stoichiometric amounts of aromatic isonitriles, formal elimination of HSi(OMe)_3 occurs, yielding the heterodinuclear isonitrile-bridged complexes [(OC)_3Fe(μ-C=N-R)(μ-dppm)Pt(PPh_3)] (6a: R = 2,6-xylyl; 6b: R = o-anisyl; 6c: R = p-anisyl; 6d: R = p-C_6H_4NH_2) and the bis(isonitrile) complexes [(OC)_2(RN≡C)Fe(μ-C=N-R)(μ-dppm)Pt(PPh_3)] (7a: R = 2,6-xylyl; 7b: R = p-anisyl). Single-crystal X-ray diffraction studies perfomed on 6a and 6b reveal that the molecular structures of these μ-isonitrile complexes closely resemble the μ-vinylidene complexes 4. The two metal centers are bridged in a symmetric manner by strongly bent CNR ligands, the aromatic groups R being oriented towards the Fe (CO)_3 moiety. Electrophilic addition of HBF_4 to the basic nitrogen atom of the μ-CNR ligand transforms 6 to the cationic μ-aminocarbyne complexes [(OC)_3Fe {μ-CN(H)R}{μ-dppm)Pt(PPh_3)][BF_4] (8a: R = 2,6-xylyl; 8b: R = p-C_6H_4NH_2).