Reduction of a CO Ligand in an Iron Phosphonate Complex with a Neutral Borane Compound. Formation of a Formyl Complex with Intramolecular Coordination to a Boron Atom

Abstract

Treatment of Cp(CO)2Fe{P(O)(OMe)2} with an electrically neutral hydroborane, 9-borabicyclo-3,3,1-nonane, yielded (1), with a terminal CO ligand reduced. The X-ray structure analysis revealed that 1 includes intramolecular coordination of the formyl oxygen to the boron atom to form a six-membered metallacycle, which would stabilize the complex as a whole.

Main Group Lewis Acid-Mediated Transformations of Transition-Metal Hydride Complexes

“…Another demonstration of Lewis acid-stabilized formyl complexes, also with iron, came from Nakazawa, Miyoshi, and co-workers in 2000. 103 They found that Cp-ligated iron phosphonate complex 64 reacts with 9-BBN to furnish stabilized formyl complex 65 (Scheme 33). This reaction is noteworthy in that the thermodynamic driving force brought on by chelation of the BBN fragment allows for a relatively weak hydride donor to be used to generate the reduced carbonyl.…”

“…Another demonstration of Lewis acid-stabilized formyl complexes, also with iron, came from Nakazawa, Miyoshi, and co-workers in 2000 . They found that Cp-ligated iron phosphonate complex 64 reacts with 9-BBN to furnish stabilized formyl complex 65 (Scheme ).…”

Anionic phosph(in)ito (“phosphoryl”) ligands: Non-classical “actor” phosphane-type ligands in coordination chemistry

“…In this reaction, 9-BBN was proposed to attack first not the carbonyl oxygen but the PO oxygen atom because of the greater polarization of the phosphonate group. In this unusual reduction of terminal CO, the  1 -P−phosphonato ligand play two important roles : (i) activation of the B-H bond in 9-BBN through the electron donation from the PO oxygen atom to the boron atom, (ii) anchoring the borane fragment to induce the strong coordination of the formyl oxygen (Scheme 39, [221]). 26 M a n u s c r i p t A c c e p t e d M a n u s c r i p t…”

“…Scheme 39.Reduction of CO ligand of  1 -P−phosphonate iron complexes 117[220] and 120[221] with boron reagents.An halogenation reaction of an amidophosphonato ligand grafted on an iron metallic fragment was reported. Addition of boron trihalides BCl 3 on P-metalated amidophosphonate complex 122 allowed the synthesis of the corresponding halogenated  1 -P−amidophosphonate complexes 123 and 124 which are good precursors for future functionalization on the organophosphorus ligand (Scheme 40,[222]) .Scheme 40.Halogenation reaction of the  1 -P−amidophosphonato ligand in iron complex 122[222].Taking into account the unique properties of O−anionic monodentate and bidentate  1 -P−phosph(in)ito ligands presented in this review, the results recently reported on the O,P-metalated phosphinite trinuclear complex 125 in which the six {Ph 2 P−O} arms bridge the Ti center with the two terminal Pd atoms[223].…”

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“…166 Reduction of the iron phosphonate complex FeCp(CO) 2 {P(O)(OMe) 2 } with 9-BBN yields FeCp(CO){C(H)OB(C 8 H 14 )OP(OMe) 2 } (Scheme 6), a formyl complex with an intramolecularly co-ordinated boron atom. 167 The facile synthesis of (triorganosilyl)pinacol boranes (SiR 3 )B(O 2 C 2 Me 4 ) has been reported (SiR 3 = SiPhMe 2 , SiPh 2 Me or SiPh 3 ). 168 The synthesis of alkali-free borosilicate gel from Si(OEt 4 ) and (MeO) 3 B 3 O 3 via rapid transesterification/oxygen transfer and elimination of B(OR) 3 has been described.…”