Diarsenic, As2, as a 4-, 6-, or 8-electron donor ligand

Abstract

Diarsenic, As,, is a versatile ligand. While it is side-on coordinated as a 4r ligand in [Cp(C0)2M]2As2 (M = Mo (4a), W (4b)), it acta as a six-electron donor in [Cp(C0)2M]2AszCr(CO)5 (M = Mo (3a) or W (3b)) or an eight-electron donor in [Cp(CO)zM]2Asz[Cr(CO)5], (M = Mo (2a) or W (2b)), respectively, by additional end-on coordination via ita lone pairs. Another form of an eight-electron donor, As2, is found for [Cp(CO)2Mn]2As-As[Mn(C0)2Cp]2 (6a), prepared by reductive -coupling of two arsinidene complexes [Cp(CO)2Mn]AsC1. In 6a Asz is bonded in a diarsinidene, &-As, valence state. As,, side-on coordinated as a six-electron donor is present in the star-type compound [(CO)&o]& (7a) obtained from Na2Mq(CO)lo and AsC13. Ita tungsten analogue [(C0)5W]3As2 reacts with iodine to give [ (CO),W,I](~-I)(p-~2-As,) (8)with a side-on coordinated four-electron donor, AS,. Syntheses and properties including structures as determined by X-ray methods are discussed.As a higher homologue of dinitrogen, diarsenic, As2, is a major constituent of arsenic vapor at high temperatures.'0276-7333185 f 2304-0326$0l.50 f 0 Even though the binding energy of this binuclear tenelectron species is quite respectable (3.93 eV),2 it is 0 1985 American Chemical Society Diarsenic as an Electron Donor Ligand

Unconventional multiple bonds: coordination compounds of unstable Vth main group ligands

“…The bond length data for such compounds are consistent with the assumption of anIXXItriple bond which is lengthened by the side on coordination (39,56,58). The synthesis of such compounds may be accomplished by the reductive coupling of XHaL educts in the periphery of suitable organometallic reagents; "-inidene" type compounds Have been shown to be the intermediates in some cases (see above (20,36,39)).…”

“…In the first step this leads to a compound containing triply bridging trigonally planar coordinated arsenic, which then, by splitting off one LnM with R3P, dimerizes to give a side on as well as end on coordinated diarsenic entity (39).…”

“…The synthesis of such compounds may be accomplished by the reductive coupling of XHaL educts in the periphery of suitable organometallic reagents; "-inidene" type compounds Have been shown to be the intermediates in some cases (see above (20,36,39)). Other approaches, starting from P4 (59) or AsH3 (24) have been developed.…”

“…(39,48,60,61) In these star type complexes the X2 entities are side on coordinated to three 16 electron fragments and would thus be expected to donate a total of six electrons to the three side on coordinated LM_fragments. Since X2 molecules are 4'IC-systems like alkines, by their 7t'-system alone they can only act as four electron donors (see above).…”

Reactivity of the Inversely Polarized Arsaalkenes R–As=C(NMe2)2 {R = [(η5‐C5Me5)(CO)2Fe], tBuC(O), 4‐Et–C6H4C(O)} towards Phosphavinylidene Complexes [η5‐(C5H5)(CO)2M=P=C(SiMe3)2] (M = Mo, W)

“…[17] Due to the π-interaction with a metal atom, the As-P distance within the 2-phospha-1-arsaallyl ligand in 4a [2.2507(7) Å] is longer than the unsupported As=P double bonds in the structurally characterized compounds {(Me 3 Si) 2 CH}As=P(2,4,6-tBu 3 C 6 H 2 ) [2.124 Å] [18] or [Cp*-(CO) 2 FeAs{Cr(CO) 5 }=P(2,4,6-tBu 3 C 6 H 2 )] [2.155(1) Å]. [19] The bond length P(1)-C(13) in 4a [1.791(2) Å]−as is also found in VI (M = Mo) [1.7875(12) Å]−is elongated with respect to a localized and unsupported P=C double bond (1.65-1.72 Å), [20] but is clearly shorter than a P-C single bond (av.…”