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Chloro complexes IrCl2(η5-C5Me5)[P(OR)3] (1) (R Me, Et) were prepared by reacting dimer [IrCl2(η5-C5Me5)]2 with phosphites in alcohol. Treatment of 1 with R1NHNH2 gave monohydrazine complexes [IrCl(η5-C5Me5)(R1NHNH2){P(OR)3}]BPh4 (2, 3, 4) [R1 H (2), Me (3), Ph (4)]. Bis(hydrazine) complexes [Ir(η5-C5Me5)(R1NHNH2)2{P(OR)3}](BPh4)2 (5, 6) were prepared by reacting chloro complexes first with AgOTf and then with an excess of hydrazine. Oxidation with Pb(OAc)4 at −40 °C of both mono- and bis(hydrazine) complexes afforded phenyldiazene derivatives [IrCl(η5-C5Me5)(PhN NH){P(OR)3}]BPh4 (7) and [Ir(η5-C5Me5)(PhN NH)2{P(OR)3}](BPh4)2 (9). Bis(aryldiazene) [Ir(η5-C5Me5)(PhN NH)2{P(OR)3}](BPh4)2 (9, 10) were also prepared by allowing hydride IrH2(η5-C5Me5)[P(OR)3] (8) to react with aryldiazonium cations [ArN2]BF4. The complexes were characterised spectroscopically and by X-ray crystal structure determination of [IrCl(η5-C5Me5)(NH2NH2){P(OEt)3}]BPh4 (2b) and [IrCl(η5-C5Me5)(CH3NHNH2){P(OEt)3}]BPh4 (3b).

Polypyridyl complexes [RuCl(η5-C5Me5)(N–N)] (1–4) [N–N 2,2′-bipyridine (bpy) (1), 4,4′-dimethyl-2,2′-bipyridine (4,4′-Me2bpy) (2), 1,10-phenanthroline (phen) (3) and 4,7-dimethyl-1,10-phenanthroline (4,7-Me2phen) (4)] were prepared by reacting [RuCl2(η5-C5Me5)]2 with Zn dust in the presence of polypyridyl ligands. Unlike the related [RuCl(η5-C5Me5)(L1)(L2)]+ [L1, L2 = P(OR)3, PPh3] derivatives with P-donor ligands, treatment of chloro compounds 1–4 with diazoalkanes Ar1Ar2CN2 afforded polypyridyl carbene complexes [Ru(η5-C5Me5)( CAr1Ar2)(N–N)]BPh4 (5–8) [Ar1 = Ar2 = Ph (a), Ar1 = Ph, Ar2 = p-tolyl (b)]. Comparative DFT studies of the formation of metallacarbenes from aromatic diazoalkanes are reported. Phosphite complex [Ru(η5-C5Me5)(bpy){P(OEt)3}]BPh4 (9) and acetylide derivatives [Ru(η5-C5Me5)(C CAr)(bpy)] (10, 11) [Ar = Ph (10), p-tolyl (11)] were also obtained by substitution of the carbene in 5–8. Unstable vinylidene cations [Ru(η5-C5Me5){ C C(H)Ar](bpy)]+ (12, 13) were formed by protonation with HBF4•Et2O of acetylide species 10, 11. The complexes were characterized spectroscopically (IR and 1H, 13C, 31P NMR) and by X-ray crystal structure determination of [Ru(η5-C5Me5){ C(Ph)(p-tolyl)}(bpy)]BPh4 (5b).

Hydrazine complexes [Ru(η5-C5H5)(RNHNH2)(PPh3){P(OMe)3}]BPh4 (1–3) and [Ru(η5-C9H7)(RNHNH2) (PPh3){P(OEt)3}]BPh4 (4–6) (R = H, Me, Ph) were prepared by allowing chloro-compounds RuCl(η5-C5H5) (PPh3)[P(OMe)3] and RuCl(η5-C9H7) (PPh3)[P(OEt)3] to react with an excess of hydrazine in refluxing ethanol. Treatment of complexes 1–6 with Pb(OAc)4 at −40 °C yielded diazene derivatives [Ru(η5-C5H5)(RN NH) (PPh3){P(OMe)3}]BPh4 (7, 8) and [Ru(η5-C9H7) (RN NH)(PPh3){P(OEt)3}]BPh4 (10, 11) (R = Me, Ph). Aryldiazene complexes [Ru(η5-C5H5)(RN NH)(PPh3){P(OMe)3}]BPh4 (8, 9) (R = Ph, p-tolyl) were also prepared by allowing hydride RuH(η5-C5H5)(PPh3)[P(OMe)3] to react with aryldiazonium salts [RN2]+BF4– in CH2Cl2. The complexes were characterised by spectroscopy (IR, 1H, 31P NMR) and X-ray crystal structure determination of [Ru(η5-C9H7)(PhNHNH2)(PPh3){P(OEt)3}]BPh4 (6).

Trichlorostannyl complex Co(SnCl3)(CO)2(PPh3)2 (1) was prepared by allowing the chloro compound CoCl(CO)2(PPh3)2 to react with SnCl2·2H2O. Instead, treatment of the iodo complex CoI(CO)2[PPh(OEt)2]2 with SnCl2·2H2O afforded a mixture of Co(SnCl2I)(CO)2[PPh(OEt)2]2 (2a) and Co(SnCl3)(CO)2[PPh(OEt)2]2 (2b) derivatives. Trichlorogermyl complexes Co(GeCl3)(CO)2L2 (3, 4) [L = PPh3, PPh(OEt)2] were prepared by allowing halo compounds CoX(CO)2L2 (X = Cl, I) to react with GeCl2·dioxane. Treatment of trihalostannyl complexes Co(SnCl2X)(CO)2L2 (1, 2) (X = Cl, I) with NaBH4 in ethanol yielded tin trihydrido derivatives Co(SnH3)(CO)2L2 (5, 6). Instead, reaction of Co(SnCl2X)(CO)2[PPh(OEt)2]2 (2) with LiAlH4 in THF yielded the hydrido CoH(CO)2[PPh(OEt)2]2 (7). Trimethylstannyl Co(SnMe3)(CO)2L2 (8, 9) and trialkynylstannyl derivatives Co[Sn(C CPh)3](CO)2L2 (10, 11) were prepared by allowing trihalostannyl compounds Co(SnCl2X)(CO)2L2 (1, 2) to react with MgBrMe and with Li+(PhC C)−, respectively, in THF. The complexes were characterised by spectroscopy (IR and 1H, 31P, 13C, 119Sn NMR) and by X-ray crystal structure determination of Co(SnCl2X)(CO)2[PPh(OEt)2]2 (2) and Co(GeCl3)(CO)2[PPh(OEt)2]2 (4).

Nitrosyl complexes [M(CO) 3 (NO)L 2 ]BPh 4 ( 2 , 5 ) [M = Mo, W; L = PPh(OEt) 2 , PPh 2 OEt] were prepared by allowing carbonyl compounds M(CO) 4 L 2 ( 1 , 4 ) to react with NOPF 6 in CH 2 Cl 2 . Dicarbonyl complex [W(CO) 2 (NO){PPh(OEt) 2 } 3 ]BPh 4 ( 7 ) was also prepared by reacting W(CO) 3 [PPh(OEt) 2 ] 3 ( 6 ) with NOPF 6 . Treatment of nitrosyl complexes 2 , 5 with [NEt 4 ]Br gave bromide derivative [MBr(CO) 2 (NO)L 2 ]BPh 4 ( 3 ). Hydrazine complexes [M(CO)(RNHNH 2 )(NO)L 3 ]BPh 4 ( 8 , 9 , 10 ) (R = H, CH 3 ) were prepared by allowing nitrosyl complexes 2 , 5 to react with hydrazine RNHNH 2 in CH 2 Cl 2 . Reaction of methylhydrazine complexes [M(CO)(CH 3 NHNH 2 )(NO)L 3 ]BPh 4 ( 8 , 10 ) with Pb(OAc) 4 at −30 °C resulted in selective oxidation of hydrazine, affording the corresponding methyldiazene derivatives [M(CO)(CH 3 N NH)(NO)L 3 ]BPh 4 ( 11 , 12 ). The complexes were characterised spectroscopically (IR and NMR), and a geometry in solution was also established.

Ethylene complexes [OsCl(η6-p-cymene)(η2-CH2 CH2)L]BPh4 (1, 2) [L = P(OMe)3, P(OEt)3, PPh(OEt)2, tBuNC) were prepared by allowing the dichloro compounds OsCl2(η6-p-cymene)L to react with CH2 CH2 in mild conditions (1 atm). Treatment of 1 with amine or hydrazine yielded [OsCl(p-tolyl-NH2)(η6-p-cymene){PPh(OEt)2}]BPh4 (3) or [OsCl(η6-p-cymene)(CH3NHNH2){PPh(OEt)2}]BPh4 (4) derivatives. The vinylidene cation [OsCl{ C C(H)Ph}(η6-p-cymene){PPh(OEt)2}]+ (5+) was also prepared from 1 and PhC CH. The complexes were characterized spectroscopically and by X-ray crystal structure determination of [OsCl(η6-p-cymene)(η2-CH2 CH2){P(OMe)3}]BPh4 (1a). The nature of the Os–ethylene bond was investigated from a computational point of view.

Hydrazine complexes [MCl(η 6 - p -cymene)(RNHNH 2 )L]BPh 4 ( 1 – 6 ) [M = Ru, Os; R = H, Me, Ph; L = P(OEt) 3 , PPh(OEt) 2 , PPh 2 OEt] were prepared by allowing dichloro complexes MCl 2 (η 6 - p -cymene)L to react with hydrazines RNHNH 2 in the presence of NaBPh 4 . Treatment of ruthenium complexes [RuCl(η 6 - p -cymene)(RNHNH 2 )L]BPh 4 with Pb(OAc) 4 led to acetate complex [Ru(κ 2 –O 2 CCH 3 )(η 6 - p -cymene)L]BPh 4 ( 7 ). Instead, the reaction of osmium derivatives [OsCl(η 6 - p -cymene)(CH 3 NHNH 2 )L]BPh 4 with Pb(OAc) 4 afforded the methyldiazenido complex [Os(CH 3 N 2 )(η 6 - p -cymene)L}]BPh 4 ( 8 ). Treatment with HCl of this diazenido complex 8 led to the methyldiazene cation [OsCl(CH 3 N NH)(η 6 - p -cymene)L}] + ( 9 + ). The complexes were characterised spectroscopically and by X-ray crystal structure determination of [OsCl(η 6 - p -cymene)(PhNHNH 2 ){PPh(OEt) 2 }]BPh 4 ( 6b ) and [Ru(κ 2 –O 2 CCH 3 )(η 6 - p -cymene){PPh(OEt) 2 }]BPh 4 ( 7b ).

Trichlorogermyl complexes M(GeCl 3 )(CO) n P 5− n ( 1–4 ) [M = Mn, Re; n = 2, 3; P = PPh(OEt) 2 ( a ), P(OEt) 3 ( b )] were prepared by allowing chloro compounds MCl(CO) n P 5− n to react with an excess of GeCl 2 •dioxane in 1,2-dichloroethane. Treatment of compounds 1–4 with LiAlH 4 in thf yielded trihydridegermyl derivatives M(GeH 3 )(CO) n P 5− n ( 5–8 ), whereas treatment of the same complexes with NaBH 4 in ethanol afforded triethoxygermyl derivatives M[Ge(OEt) 3 ](CO) n P 5− n ( 9–11 ). Trimethylgermyl compounds M(GeMe 3 )(CO) n P 5− n ( 12, 13 ) and the alkynylgermyl derivative Mn[Ge(C CPh) 3 ](CO) 3 [PPh(OEt) 2 ] 2 ( 14a ) were also prepared by allowing trichlorogermyl compounds 1–4 to react with either MgBrMe or Li + C CPh − , respectively, in thf. Treatment of compound Re(GeCl 3 )(CO) 3 [PPh(OEt) 2 ] 2 ( 4a ) with SnCl 2 •2H 2 O gave the stannyl-germyl derivative Re[GeCl 2 (SnCl 3 )](CO) 3 [PPh(OEt) 2 ] 2 ( 15a ). The complexes were characterised by spectroscopy and X-ray crystal structure determination of 4a , 5a , and 13a .

p-Cymene complexes MCl2(η6-p-cymene)L [M = Ru, Os; L = P(OEt)3, PPh(OEt)2, (CH3)3CNC] were prepared by allowing [MCl(μ-Cl)(η6-p-cymene)]2 to react with phosphites or tert-butyl isocyanide. Treatment of MCl2(η6-p-cymene)L complexes with 1,3-ArN NN(H)Ar triazene and an excess of NEt3 gave the cationic triazenide derivatives [M(η2-1,3-ArNNNAr)(η6-p-cymene)L]BPh4 (Ar = Ph, p-tolyl). Neutral triazenide complexes MCl(η2-1,3-ArNNNAr)(η6-p-cymene) (M = Ru, Os) were also prepared by allowing [MCl(μ-Cl)(η6-p-cymene)]2 to react with 1,3-diaryltriazene in the presence of triethylamine. p-Cymene complexes MCl2(η6-p-cymene)L reacted with equimolar amounts of 1,3-ArN NN(H)Ar triazene to give both triazenide complexes [M(η2-1,3-ArNNNAr)(η6-p-cymene)L]BPh4 and amine derivatives [MCl(ArNH2)(η6-p-cymene)L]BPh4. A reaction path for the formation of the amine complex is also reported. The complexes were characterised by spectroscopy and X-ray crystallography of RuCl2(η6-p-cymene)[PPh(OEt)2] and [Ru(η2-1,3-p-tolyl-NNN-p-tolyl)(η6-p-cymene){CNC(CH3)3}]BPh4. Selected triazenide complexes were studied as catalysts in the hydrogenation of 2-cyclohexen-1-one and cinnamaldehyde.

Hydride complex RuH 2 (PFFP) 2 ( 1 ) [PFFP = (CF 3 CH 2 O) 2 PN(CH 3 )N(CH 3 )P(OCH 2 CF 3 ) 2 ] was prepared by allowing the compound RuCl 4 (bpy) · H 2 O (bpy = 1,2-bipyridine) to react first with the phosphite PFFP and then with NaBH 4 . Chloro-complex RuCl 2 (PFFP) 2 ( 2 ) was also prepared, either by reacting RuCl 4 (bpy) · H 2 O with PFFP and zinc dust or by substituting triphenylphosphine with PFFP in the precursor complex RuCl 2 (PPh 3 ) 3 . Hydride derivative RuH 2 (POOP) 2 ( 3 ) (POOP = Ph 2 POCH 2 CH 2 OPPh 2 ) was prepared by reacting compound RuCl 3 (AsPh 3 ) 2 (CH 3 OH) first with the phosphite POOP and then with NaBH 4 . Depending on experimental conditions, treatment of carbonylated solutions of RuCl 3 · 3H 2 O with POOP yields either the cis - or trans -RuCl 2 (CO)(PHPh 2 )(POOP) ( 4 ) derivative. Reaction of both cis - and trans - 4 with LiAlH 4 in thf affords dihydride complex RuH 2 (CO)(PHPh 2 )(POOP) ( 5 ). Chloro-complex all - trans -RuCl 2 (CO) 2 (PPh 2 OMe) 2 ( 6 ) was obtained by reacting carbonylated solutions of RuCl 3 · 3H 2 O in methanol with POOP. Treatment of chloro-complex 6 with NaBH 4 in ethanol yielded hydride derivative all - trans -RuH 2 (CO) 2 (PPh 2 OMe) 2 ( 7 ). The complexes were characterised spectroscopically and the X-ray crystal structures of complexes 1 , 3 , cis - 4 and 6 were determined.

Mixed-ligand OsCl(Tp)L(PPh3) complexes 1 [Tp = hydridotris(pyrazolyl)borate; L = P(OMe)3, P(OEt)3 and PPh(OEt)2] were prepared by allowing OsCl(Tp)(PPh3)2 to react with an excess of phosphite. Treatment of chlorocomplexes 1 with NaBH4 in ethanol afforded hydride OsH(Tp)L(PPh3) derivatives 2. Stable dihydrogen [Os(η2-H2)(Tp)L(PPh3)]BPh4 derivatives 3 were prepared by protonation of hydrides 2 with HBF4 · Et2O at −80 °C. The presence of the η2-H2 ligand is supported by short T1 min values and JHD measurements on the partially deuterated derivatives. Treatment of the hydride OsH(Tp)[P(OEt)3](PPh3) complex with the aryldiazonium salt [4-CH3C6H4N2]BF4 afforded aryldiazene [Os(4-CH3C6H4NNH)(Tp){P(OEt)3}(PPh3)]BPh4 derivative 4. Instead, aryldiazenido [Os(4-CH3C6H4N2)(Tp)[P(OEt)3](PPh3)](BF4)2 derivative 5 was obtained by reacting the hydride OsH(Tp)[P(OEt)3](PPh3) first with methyltriflate and then with aryldiazonium [4-CH3C6H4N2]BF4 salt. Spectroscopic characterisation (IR, 15N NMR) by the 15N-labelled derivative strongly supports the presence of a near-linear Os–NN–Ar aryldiazenido group. Imine [Os{η1-NHC(H)Ar}(Tp){P(OEt)3}(PPh3)]BPh4 complexes 6 and 7 (Ar = C6H5, 4-CH3C6H4) were also prepared by allowing the hydride OsH(Tp)[P(OEt)3](PPh3) to react first with methyltriflate and then with alkylazides.

Pyrazole IrHCl 2 (HRpz)P 2 [P = PPh 3 , P i Pr 3 ; R = H, 3-Me], bis(pyrazole) [IrHCl(HRpz) 2 (PPh 3 ) 2 ]BPh 4 and imidazole IrHCl 2 (HIm)(PPh 3 ) 2 derivatives were prepared by allowing the IrHCl 2 (PPh 3 ) 3 complex to react with the appropriate azole in refluxing 1,2-dichloroethane. Nitrile IrHCl 2 (CH 3 CN)(PPh 3 ) 2 and 2,2′-bipyridine (bpy) [IrHCl(bpy)(PPh 3 ) 2 ]BPh 4 derivatives were also prepared using IrHCl 2 (PPh 3 ) 3 as a precursor. The complexes were characterised spectroscopically (IR and NMR) and a geometry in solution was also established. Protonation with Bronsted acid of pyrazole IrHCl 2 (Hpz)(PPh 3 ) 2 and imidazole IrHCl 2 (HIm)(PPh 3 ) 2 complexes proceeded with the loss of the azole ligands and the formation of the unstable IrHCl 2 (PPh 3 ) 2 derivative. Vinyl IrCl 2 {CH C(H)R1}(HRpz)P 2 and IrCl 2 {CH C(H)R1}(HIm)P 2 (R1 = Ph, p- tolyl, COOCH 3 ; P = PPh 3 , P i Pr 3 ) complexes were prepared by allowing hydride-pyrazole IrHCl 2 (HRpz)P 2 and hydride-imidazole IrHCl 2 (HIm)P 2 to react with an excess of terminal alkyne in 1,2-dichloroethane. The complexes were characterised spectroscopically and by the X-ray crystal structure determination of the IrCl 2 {CH C(H)Ph}(Hpz)(PPh 3 ) 2 derivative.

Dithioformato [Re{η 2 -SC(H)S}(NO)P 3 ]BPh 4 ( 1 ), thioformamido [Re{η 2 -RNC(H)S}(NO)P 3 ]BPh 4 ( 2 ) (R = Et, p -tolyl), formamido [Re{η 2 -PhNC(H)O}(NO)P 3 ]BPh 4 ( 3 ) and formamidinato [Re{η 2 - p -tolylNC(H)N p -tolyl}(NO)P 3 ]BPh 4 ( 4 ) (P = PPh 2 OEt) complexes were prepared by allowing the hydride ReH 2 (NO)P 3 to react first with triflic acid and then with the appropriate heteroallene CS 2 , RNCS, PhNCO and p -tolylNCN p -tolyl. Treatment of the ReH 2 (NO)L(PPh 3 ) 2 [L = P(OEt) 3 , PPh(OEt) 2 ] and ReH 2 (NO)(PPh 3 ) 3 hydrides first with triflic acid and then with isothiocyanate RNCS (R = Et, p -tolyl) gave the [Re{η 2 -RNC(H)S}(NO){P(OEt) 3 }(PPh 3 ) 2 ]BPh 4 ( 5 , 6 ) and [Re(η 2 -RNC(H)S)(NO)(PPh 3 ) 3 ]BPh 4 ( 7 ) derivatives. Depending on the nature of the phosphite, instead, the reaction of ReH 2 (NO)L(PPh 3 ) 2 and ReH 2 (NO)(PPh 3 ) 3 hydrides first with CF 3 SO 3 H and then with isocyanate R1NCO (R1 = Ph, p -tolyl) gave the chelate [Re{η 2 -R1NC(H)O}(NO){P(OEt) 3 }(PPh 3 ) 2 ]BPh 4 ( 8 ) and [Re{η 2 -R1NC(H)O}(NO)(PPh 3 ) 3 ]BPh 4 ( 10 ) complexes with P(OEt) 3 or PPh 3 , while the η 1 -coordinate [Re{η 1 -RNC(H)S}(NO){PPh(OEt) 2 } 2 (PPh 3 ) 2 ]BPh 4 ( 9 ) derivative was obtained with the PPh(OEt) 2 phosphite ligand. η 1 -Coordinate dithioformato [Re{η 1 -SC(H) S}(NO){PPh(OEt) 2 } 2 (PPh 3 ) 2 ]BPh 4 ( 11 ) and formato [Re{η 1 -OC(H) O}(NO){PPh(OEt) 2 } 2 (PPh 3 ) 2 ]BPh 4 ( 12 ) complexes, as well as the formamidinato [Re{η 2 - p -tolylNC(H)N p -tolyl}(NO){P(OEt) 3 }(PPh 3 ) 2 ]BPh 4 ( 13 ) derivative were also prepared.

Chloro phosphite complexes RuClTpL(PPh 3 ) ( 1a , 1b ) [L = P(OEt) 3 , PPh(OEt) 2 ] and RuClTp[P(OEt) 3 ] 2 ( 1c ) [Tp = hydridotris(pyrazolyl)borate] were prepared by allowing RuClTp(PPh 3 ) 2 to react with an excess of phosphite. Treatment of the chloro complexes 1 with NaBH 4 in ethanol yielded the hydride RuHTpL(PPh 3 ) ( 2a , 2b ) and RuHTp[P(OEt) 3 ] 2 ( 2c ) derivatives. Protonation reaction of 2 with Bronsted acids was studied and led to thermally unstable (above 10 °C) dihydrogen [Ru(η 2 - H 2 )TpL(PPh 3 )] + ( 3a , 3b ) and [Ru(η 2 -H 2 )Tp{P(OEt) 3 } 2 ] + ( 3c ) complexes. The presence of the η 2 -H 2 ligand is indicated by short T 1 min values and J HD measurements of the partially deuterated derivatives. Aquo [RuTp(H 2 O)L(PPh 3 )]BPh 4 ( 4 ), carbonyl [RuTp(CO)L(PPh 3 )]BPh 4 ( 5 ), and nitrile [RuTp(CH 3 CN)L(PPh 3 )]BPh 4 ( 6 ) derivatives [L = P(OEt) 3 ] were prepared by substituting H 2 in the η 2 -H 2 derivatives 3 . Vinylidene [RuTp{ C C(H)R}L(PPh 3 )]BPh 4 ( 7 , 8 ) (R = Ph, t Bu) and allenylidene [RuTp( C C CR1R2)L(PPh 3 )]BPh 4 ( 9 – 11 ) complexes (R1 = R2 = Ph, R1 = Ph R2 = Me) were also prepared by allowing dihydrogen complexes 3 to react with the appropriate HC CR and HC CC(OH)R1R2 alkynes. Deprotonation of vinylidene complexes 7 , 8 with NEt 3 was studied and led to acetylide Ru(C CR)TpL(PPh 3 ) ( 12 , 13 ) derivatives. The trichlorostannyl Ru(SnCl 3 )TpL(PPh 3 ) ( 14 ) compound was also prepared by allowing the chloro complex RuClTpL(PPh 3 ) to react with SnCl 2 · 2H 2 O in CH 2 Cl 2 .

Depending on experimental conditions and the nature of the phosphite, the reaction of OsH2P4 [P=P(OEt)3 and PPh(OEt)2] with bis(aryldiazonium) salts [N2Ar–ArN2](BF4)2 [Ar–Ar=4,4′-C6H4–C6H4, 4,4′-(2-CH3)C6H3–C6H3(2-CH3), 4,4′-C6H4–CH2–C6H4 and 1,5-C10H6] afford the cis and the trans binuclear [{OsHP4}2(μ-HN=NAr–ArN=NH)](BPh4)2 1, 2 aryldiazene derivatives. These complexes 1, 2 further react with the mono(diazonium) (4-CH3C6H4N2)BF4 salt to give the bis(aryldiazene) [{Os(4-CH3C6H4N=NH)P4}2(μ-HN=NAr–ArN=NH)](BPh4)4 3, 4 derivatives. Binuclear bis(aryldiazenido) [{OsP4}2(μ-N2Ar–ArN2)](BPh4)2 (6) [P=P(OEt)3; Ar–Ar=4,4′-C6H4–C6H4, 4,4′-C6H4–CH2–C6H4] complexes were prepared by deprotonating with NEt3 the nitrile-diazene [{Os(4-CH3C6H4CN)P4}2(μ-HN=NAr–ArN=NH)](BPh4)4 (5) derivatives. The aryldiazenido compounds 6 react with HCl to give the new aryldiazene [{OsClP4}2(μ-HN=NAr–ArN=NH)](BPh4)2 (7) derivatives. The characterisation of the complexes by IR and 1H, 31P, 15N NMR data is also discussed. The reaction of the hydride OsH2(PPh2OEt)4 with mono(diazonium) salts was also studied and led exclusively to the mono(aryldiazene) [OsH(ArN= NH)(PPh2OEt)4]BPh4 (8) (Ar=C6H5, 4-CH3C6H4) derivatives. Spectroscopic data (1H, 31P, 15N NMR) on 15N-labelled derivatives suggest the presence of two isomers with the N-bonded and the π-bonded ArN=NH ligand, respectively.

Aryldiazene complexes [Rh(ArNNH)(CO)(PPh3)3]BF4 (1) and [Rh(ArNNH)(PPh3)4]BF4 (2) (Ar=C6H5 or 4-CH3C6H4) were prepared by allowing hydride species RhH(CO)(PPh3)3 and RhH(PPh3)4 to react with aryldiazonium cations at low temperature. The complexes were characterised by IR and 1H-, 31P- and 15N-NMR spectra, using 15N labelled compounds. Free aryldiazene ArNNH species and [Rh{PPh(OEt)2}4]BF4 were obtained by reacting the hydride RhH[PPh(OEt)2]4 with aryldiazonium cations in CH2Cl2 at −80°C. Reactions of aryldiazene complexes 1 and 2 with H2 (1 atm) were also studied, but did not lead to arylhydrazine derivatives.

Treatment of [Re(η2-H2)(CO)2P3]+ cations with phenylacetylene leads to the displacement of H2 and the formation of vinylidene [Re{CC(H)Ph}(CO)2P3]+ (1–3) [P=P(OEt)3, PPh(OEt)2 or PPh2OEt] derivatives. Infrared and NMR data support equilibrium in solution [Re(CO)2P3]++PhCCH⇄[Re{CC(H)Ph}(CO)2P3]+ involving the unsaturated complex, free alkyne and vinylidene derivative. 1,4-Diethynylbenzene also tautomerises to the Re(I) centre, affording the [Re{CC(H)(1,4-C6H4CCH)}(CO)2P3]BF4 [P=P(OEt)3 or PPh(OEt)2] vinylidene derivatives. Vinylidene complexes 1–3 are deprotonated easily by NEt3 to give acetylides Re(CCR)(CO)2P3 (4–6) (R=Ph or 1,4-C6H4CCH), which may in turn be reprotonated with HBF4·Et2O to reform vinylidenes 1–3. Acetylide complexes 4–6 were also prepared by reacting unsaturated cations [Re(CO)2P3]+ with lithium acetylide. Binuclear complexes {Re(CO)2P3}2(μ-1,4-CCC6H4CC) (7, 8) [P=PPh(OEt)2 or PPh2OEt] were obtained by sequential treatment of [Re(CO)2P3]+ cations, first with 1,4-HCCC6H4CCH and then with an excess of NEt3. Propadienylidene complexes [Re(CCCPh2)(CO)2P3]BF4 (9, 10) [P=PPh(OEt)2 or PPh2OEt] were prepared by allowing [Re(η2-H2)(CO)2P3]+ cations or unsaturated species [Re(CO)2P3]+ to react with HCCC(Ph2)OH at room temperature. The characterisation of all new complexes by IR and 1H-, 31P{1H}- and 13C{1H}-NMR spectra is also discussed.

Monoacetylide RuCl(CCR)P 4 complexes (R=Ph, 4-MeC 6 H 4 , 1,4-C 6 H 4 CCH, SiMe 3 , Bu t or COOMe; P=P(OEt) 3 or P(OMe) 3 ) were prepared by allowing RuCl 2 P 4 to react with terminal alkynes RCCH in the presence of an excess of NEt 3 . Dinuclear compounds [{Ru[P(OEt) 3 ] 5 } 2 (μ-1,4-CCC 6 H 4 CC)]Y 2 (Y=PF 6 or BPh 4 ) were also prepared from the reaction of RuCl 2 P 4 with 1,4-HCCC 6 H 4 CCH. Treatment of RuCl 2 P 4 with Li + [1,4-HCCC 6 H 4 CC] − afforded bis(alkynyl) Ru(1,4-CCC 6 H 4 CCH) 2 P 4 [P=P(OEt) 3 , P(OMe) 3 or PPh(OEt) 2 ] derivatives. Protonation reactions of monoacetylides RuCl(CCR)P 4 with CF 3 SO 3 H led to vinylidene [RuCl{CC(H)R}P 4 ]CF 3 SO 3 [R=Ph, 4-MeC 6 H 4 or 1,4-C 6 H 4 CCH; P=P(OEt) 3 or P(OMe) 3 ] complexes, which were fully characterised by IR and 1 H-, 31 P- and 13 C-NMR spectra.

The reaction of NO with [CoXL 4 ] + (X = Cl, Br, I; L = phosphites) cations has been studied and new pentacoordinated mono- and tetracoordinated dinitrosyl cobalt complexes, {MNO} 8 and {M(NO) 2 } 10 , obtained in mild conditions. Trigonal-bipyramidal structures with linear MNO have been deduced from infrared and pmr spectra for the mononitrosyl compounds described. The reactivity with phosphine, CO, halogen, and isocyanide of the nitrosyl complexes reported is also presented as well as the investigations carried out to ascertain the species operating the reduction to cobalt(I) in the formation of dinitrosyl complexes.

Electronic absorption spectra of M(CNPh) 6 [M = Cr(0), Mo(0), W(0)], [Mn(CNPh) 6 ]Cl, and [Mn (CNPh) 6 ](PF 6 ) 2 are reported. Each of the M(CNPh) 6 complexes exhibits three intense metal-to-ligand charge transfer (MLCT) absorption bands between 20.8 and 32.7 kK. The lowest MLCT bands are observed at 29.9 and 31.1 kK in the electronic spectrum of Mn (CNPh) 6 + . Low energy bands at 18.2 and 20.4 kK in [Mn(CNPh) 6 ] 2+ are assigned to vibronic components of a σ(CNPh) → dπ charge transfer transition. The unique electronic structural properties of arylisocyanide complexes are apparently related to the π conjugation of aromatic ring orbitals with the out-of-plane π*(CN) function.

The complexes [Ru(ArNNH)(RNC){P(OEt) 3 } 4 ](BPh 4 ) 2 ( 1 : Ar = 4-CH 3 C 6 H 4 , 4-CH 3 OC 6 H 4 , 4-FC 6 H 4 ; R = 4-CH 3 C 6 H 4 , 4-CH 3 OC 6 H 4 , C 6 H 5 ), [Ru(RNC) 2 -{P(OEt) 3 } 4 ] (BPh 4 ) 2 ( 2 ) and [Ru(RNC) 3 {P(OEt) 3 } 3 ](BPh 4 ) 2 ( 3 ) (R = 4-CH 3 -C 6 H 4 derivatives were prepared by treating the bis(diazene) [Ru(ArNNH) 2 -{P(OEt) 3 } 4 ] 2+ cations with isocyanides: they were characterized by IR and 1 H and 31 P{ 1 H} NMR spectroscopy. The crystal structure of [Ru(4-CH 3 C 6 H 4 NNH)(4-CH 3 C 6 H 4 NC){P(OEt) 3 }4] (PF 6 ) 2 was determined by X-ray diffraction. Crystals are monoclinic, of space group P 2 1 / n with unit-cell dimensions a 23.527(4), b 22.597(3), c 11.565(1) A, β 92.78(1)°, and Z = 4. The structure was solved by the heavy-atom method and refined by least-squares procedures to an R value of 0.0906 for 4812 independent observed reflections. The ruthenium atom lies within an essentially octahedral array of ligands with the diazene and isocyanide groups cis to one another. Reactions of the mono(diazene) derivatives 1 with NaBH 4 and LiCl gave the new complexes [RuH(ArNNH)(RNC){P(OEt) 3 }3]BPh 4 and [RuCl(RNC){P(OEt) 3 } 4 ]BPh 4 .

The reactions of bromomalonaldehyde anion (BMA) with several metal(II) chlorides have been studied and the syntheses of the tris(chelate) AsPh 4 [Fe(BMA) 3 ] complex and the complexes [M(BMA) 2 (H 2 O) 2 ] and [M(BMA) 2 ] (M  Fe II , Co II , Ni II , Cu II ) are reported. Complexes CoBr 2 (CNR) 4 , [FeBr(CNR) 5 ]BPh 4 and [Cu(CNR) 4 ]Br (R  4-CH 3 C 6 H 4 ) were obtained by reaction of the BMA derivatives with RNC.

Solution and solid state electronic spectral measurements at 295, 77 and 7° K, have been carried out on the low spin five-coordinate [CO I (CO) 2 {P(C 6 H 5 )(OC 2 H 5 ) 2 } 3 ][B(C 6 H 5 ) 4 ] (I) and CO I I(CO) 2 {P(C 6 H 5 )(OC 2 H 5 ) 2 } 2 (II). The presence of two moderately intense ligand field bands at respectively 27.4 (e EPA = 420) and 30.5 kK (e EPA = 980) for (I) and 22.6 (e EPA = 650) and 26.0 kK (e EPA = 1700) for (II) is consistent with a trigonal bipyramidal geometry of C 2v symmetry for both complexes. Allowed I»Co(I) charge transfer bands are observed at 29.0 kK and 34.5 kK for (II), whereas an allowed P(C 6 H 5 )(OC 2 H 5 ) 2 »Co(I) is found at 39.6 kK for (1) and 40.0 kK for (II).