Phosphine−Boranes as Bidentate Ligands:  Formation of [8,8-η²-{η²-(BH₃)·dppm}-nido-8,7-RhSB₉H₁₀] and [9,9-η²-{η²-(BH₃)·dppm}-nido-9,7,8-RhC₂B₈H₁₁] from [8,8-(η²-dppm)-8-(η¹-dppm)-nido-8,7-RhSB₉H₁₀] and [9,9-(η²-dppm)-9-(η¹-dppm)-nido-9,7,8-RhC₂B₈

Abstract

The two clusters [8,8-(eta(2)-dppm)-8-(eta(1)-dppm)-nido-8,7-RhSB(9)H(10)] (1) and [9,9-(eta(2)-dppm)-9-(eta(1)-dppm)-nido-9,7,8-RhC(2)B(8)H(11)] (2) (dppm = PPh(2)CH(2)PPh(2)), both of which contain pendant PPh(2) groups, react with BH(3).thf to afford the species [8,8-eta(2)-(eta(2)-(BH(3)).dppm)-nido-8,7-RhSB(9)H(10)] (3) and [9,9-eta(2)-(eta(2)-(BH(3)).dppm))-nido-9,7,8-RhC(2)B(8)H(11)] (4), respectively. These two species are very similar in that they both contain the bidentate ligand [(BH(3)).dppm], which coordinates to the Rh center via a PPh(2) group and also via a eta(2)-BH(3) group. Thus, the B atom in the BH(3) group is four-coordinate, bonded to Rh by two bridging hydrogen atoms, to a terminal H atom, and to a PPh(2) group. At room temperature, the BH(3) group is fluxional; the two bridging H atoms and the terminal H atom are equivalent on the NMR time scale. The motion is arrested at low temperature with DeltaG++ = ca. 37 and 42 kJ mol(-1), respectively, for 3 and 4. Both species are characterized completely by NMR and mass spectral measurements as well as by elemental analysis and single-crystal structure determinations.

Organometallic chemistry on rhodaheteroborane clusters: reactions with bidentate phosphines and organotransition metal reagents

“…This satisfies the metal center electronically and also maintains the correct nido-skeletal electron count of the cluster; the ligand functions as a six-electron donor. 18 is thus similar to the species [8,8-η 2 -{(η 2 -BH 3 )(dppm)}-nido-8,7-RhSB 9 H 10 ] (6) described above, 14,15 and shown in Scheme 5. The latter contains a BH 3 · dppm moiety that functions as a multidentate ligand, but in that case the BH 3 group uses two of its hydrogen atoms in three-center twoelectron bonds to rhodium, whereas in 18 the interactions are normal two-electron two-center bonds.…”

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

“…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).…”

Reactions of Boranes and Metallaboranes with Phosphines

“…We have developed the chemistry of VIII and discovered that it and its derivatives are not as easy to work with as IX. Thus, reaction of III with other bidentate bases gave products difficult to character- [12]. The species X and XI, whose formation is shown in Scheme 2 are quite similar in that they contain ligands which bond to the Rh through a donor P atom and also via two bridging atoms such that the ligand supplies 6 electrons to the cluster.…”