Ruthenium (II) complexes of the chelating phosphine borane H2ClB·dppm

Chelating Phosphane–Boranes as Hemilabile Ligands – Synthesis of[Mn(CO)3(η2‐H3B·dppm)][BArF4] and [Mn(CO)4(η1‐H3B·dppm)][BArF4]

“…Within the limits of confidence associated with the location of hydrides by X-ray crystallography the two hydrogen atoms that bridge to the metal atom have B-H bonds that can be considered longer than that to the terminal hydride [B1-H1a 1.07(3) Å, B1-H1b 1.30(4) Å, B1-H1c 1.24(3) Å], consistent with the 3c-2e bond description. The Mn-B distance is short [2.146(4) Å] mirroring that observed in the ruthenium complexes I and II, [16,18] being slightly longer than that found in three-coordinate boryl complexes of Mn such as (CO) 5 -MnB(O 2 C 6 H 4 ) [2.108(6) Å] [22] and comparable with the σ-…”

“…[24] As for I and II, [16,18] this interaction in 1 is best described as being like borohydride and not a dihydridoboryl complex, as the B-Mn-H and H-Mn-H angles are far more compressed than expected for a complex with two hydrides and a boryl ligand. [25] As expected for a relatively weakly bound BH 3 group, the M-C bond lengths associated with the carbonyl ligands trans to the bridging hydrides [Mn-C2 1.803(4) Å and Mn-C3 1.817(4) Å] are shorter than that trans to the phosphane group [Mn-C1 1.849(4) Å].…”

“…Treatment of Mn(CO) 5 Br with H 3 B·dppm using Na[BAr [18] only resulted in mixtures of intractable products. Complex 1 has been fully characterised by NMR spectroscopy and X-ray crystallography, which all show that the chelating phosphane-borane adopts a bidentate (η 2 ) bridging mode of the BH 3 group.…”

“…One way of preventing borane loss would be to include the borohydride ligand in a chelate ring, allowing this potentially useful η 2 -to η 1 -transformation to occur without decomposition. Others [14,15] and we [16][17][18] have recently reported on the coordination chemistry of chelating phosphane-boranes XH 2 B·dppm (X = H, Cl, dppm = PPh 2 CH 2 PPh 2 ) in which one end of the ligand is valenceisoelectronic with borohydride while the other provides a firm phosphane anchor to the metal centre. (Scheme 2).…”

“…(Scheme 2). [16,18] With these strong ligands the reaction is not reversible, and the ligand cannot be removed. The η 2 -precursors I and II can thus be considered as being operationally unsaturated, effectively acting as a source of a reactive cationic 16-electron {RuCp*(η 1 -XH 2 B·dppm)} + fragment.…”