Reactivity of silyl-substituted heterobimetallic iron-platinum hydride complexes towards unsaturated molecules, I - Alkyne insertions into the platinum-hydride bond, phosphane-induced sigma-alkenyl-mu-vinylidene rearrangements and formation of mu-isonitrile complexes

The heterobimetallic hydride complexes [(OC)(3)Fe{Si(OMe)(3)}(mu-Ph2PXPPh2) Pt(H) (PR3)] (1a: X = CH2, PR3 = PPh3; 1b: X = NH, PR3 = PPh3; 1c: X = CH2, PR3 = PMePh2) have been prepared by the oxidative addition of [(OC)(3)Fe(H ){Si(OMe)(3)}(eta(1)-Ph2PXPPh2)] to [Pt(H2C=CH2)(PPh3)(2)] or by reaction o f K[(OC)(3)Fe{Si(OMe)(3)}(eta(1)-dppm)] with trans-[Pt(Cl) (H) (PPh3)(2)]. The solid-state structure of compound Ib has been determined by single-crys tal X-ray diffraction. 1-Alkynes such as methylpropiolate or phenylacetylen e insert in a regiospecific manner into the Pt-H bond of 1 to yield the sig ma-alkenyl complexes [(OC)(3)Fe{mu-Si(OMe)(2)(OMe)}(mu-Ph2PXPPh2)Pt{C(R)=CH 2}] (2a: X=CH2, R = CO2Me; 2b: X = NH, R = CO2Me; 3a: X = CH2, R = Ph). Add ition of the Pt-H bond of 3a across the triple bond of [D-1]phenylacetylene affords [(OC)(3)Fe{mu-Si(OMe)(2)(OMe)}(mu-dppm)Pt{C(Ph)=C(D)H}] (3a*) havi ng the deuteron trans to platinum (cis addition). This insertion reaction i s accompanied by dissociation of the platinum-bonded PR3 ligand and saturat ion of the vacant coordination site by a dative mu-eta(2)-Si-O-->Pt interac tion. When 3 is treated with PR3 again, a subsequent phosphane-induced rear rangement leading to vinylidene-bridged complexes [(OC)(3)Fe{mu-C=C(H)R'}(m u-Ph2PXPPh2)Pt(PR3)] (4a: X = CH2, R' = Ph, PR3 = PPh3; 4b: X = NH, R' = Ph , PR3 = PPh3; 4c: X = CH2, R' = Ph, PR3 = PMePh2; 4d: X = CH2, R' = p-tolyl , PR3 = PPh3) occurs. Upon purging a solution of 3a with carbon monoxide, t he labile CO adduct [(OC)(3)Fe{Si(OMe)(3)}(mu-dppm)Pt(CO){C(Ph)=CH2}] 5a is formed, addition of 2,6-xylyl isocyanide to 2a and 3a affords the isonitri le adducts [(OC)(3)Fe{Si(OMe)(3)} (mu-dppm)Pt(CNxylyl){C(R)=CH2}] (5b: R = CO2Me; 5c: R = Ph), respectively. When hydride complex la is allowed to rea ct with stoichiometric amounts of aromatic isonitriles, formal elimination of HSi(OMe)(3) occurs, yielding the heterodinuclear isonitrile-bridged comp lexes [(OC)(3)Fe(mu-C=N-R)(mu-dppm)Pt(PPh3)] (6a: R = 2,6-xylyl; 6b: R = o- anisyl; 6c: R = p-anisyl; 6d: R = p-C6H4NH2) and the bis(isonitrile) comple xes [(OC)(2)(RN=C)Fe(mu-C=N-R)(mu-dppm)Pt(PPh3)] (7a: R = 2,6-xylyl; 7b: R = p-anisyl). Single-crystal X-ray diffraction studies performed on 6a and 6 b reveal that the molecular structures of these mu-isonitrile complexes clo sely resemble the mu-vinylidene complexes 4, The two metal centers are brid ged in a symmetric manner by strongly bent CNR ligands, the aromatic groups R being oriented towards the Fe(CO)(3) moiety. Electrophilic addition of H BF4 to the basic nitrogen atom of the mu-CNR ligand transforms 6 to the cat ionic mu-aminocarbyne complexes [(OC)(3)Fe{mu-CN(H)R}(mu-dppm)Pt(PPh3)][BF4 ] (8a: R = 2,6-xylyl; 8b: R = p-anisyl; 8c: R = p-C6H4NH2).