Stereochemically matched (and mismatched) bisphosphine ligands: DIOP-DIPAMP hybrids

Abstract

The three diastereomers of (JZ^t)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis([2-methoxyphenyl]phenylphosphino)butane (1) and of (fJ^?)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis ([2-(dimethylammo)phenyl]phenylphosphino)butane (2) have been prepared and isolated. Advanced intermediates in the preparation and isolation of diastereomers of (fi^Z)-2,3-0-isopropylidene-2,3-dihydroxy-l,4-bis ([2,6dimethoxyphenyl]phenylphosphino)butane (3) are also described. Absolute configurations of four of the chiral phosphine ligands were determined via single-crystal X-ray diffraction studies of molybdenum tetracarbonyl derivatives ((RPJ1P)•6, (RPJlP)-7, (RPJ1P)-S, and (SP,SP)-8); this facilitated assignments of absolute configurations for all the isomers of ligands 1-3. These bisphosphine ligands are rare insofar as they have chiral phosphorus centers supported on an asymmetric carbon framework. Several reactions were performed to test for "cooperativity" between chiral centers in these ligands with respect to asymmetric induction in transition-metal-catalyzed processes. Matching and mismatching effects were observed, but there are some irregular trends in the data. The enantioselectivities obtained were moderate but greater than that for the parent ligand DIOP in some cases. The o-dimethylamino functionality of ligands 2 may play an active role in the coordination of these isomeric bisphosphine ligands. Trends and factors influencing the performance of ligands 1-3 in asymmetric catalysis are discussed. Crystal data for the compounds analyzed via X-ray diffraction are as follows. (RPJlP)•6: monoclinic, space group 2 (No. 4), o = 11.621

The Development of Enantioselective Rhodium-Catalysed Hydroboration of Olefins

“…Extending the range of hydroboration-oxidation substrates to include indene (31) and styrene (38) gave 1-indanol (36) and 1-phenylethanol (39), respectively, with the same sense of asymmetric induction irrespective of the chirality at phosphorus, showing that it was the chirality of the carbon backbone that controlled the asymmetry of the reaction, Table 7. [95] There was no correlation in these experiments between the chirality at phosphorus and that at carbon and attempts to produce "matched" and "mismatched" catalysts were not successful.…”

“…[11,87] "Asymmetric amplification" experiments provided no evidence to suggest there was more than one phosphine ligand per catalyst molecule but did not conclusively rule out that possibility either. [94] Subsequently, Burgess [95] prepared a series of hybrid ligands 51 -53, Figure 5, which were chiral not only in the carbon backbone like (R,R)-DIOP (24), but also at phosphorus, like DIPAMP (50).…”

P-Alkylated (1S,2S)-Cyclopentane-1,2-diylbisphosphanes with Four Stereogenic Centers and Some Group 10 Metal(II) Complexes Containing the (1S,2S)-C5H8[P(CH3)C8H15-cyclo]2 Ligand

“…(1S,2S)-C 5 H 8 (PH) 2 [1] , across the carbonϪcarbon double bonds of cycloalkenes containing five to eight ring atoms provides an attractive method for the synthesis of the preparation of asymmetric bis(secondary phosphanes). The latter can be derivatized further by metalation and alkylation to give bis(tertiary) P 2 [15] . None of these contains peralkylated phosphanyl substituents ϪP(RЈ)R. It was therefore a challenge to isolate the S P ,S PЈ -configurated diastereomer 6a, observed to predominate in the isomeric mixture of bisphosphanes 6aϪc, in optically pure form.…”

“…The three diastereomers of the peralkylated chiral P 2 ligand (1S,2S)-C 5 H 8 [P(CH 3 )C 8 H 15 cyclo] 2 and its complexes with NiCl 2 , PdI 2 , and PtI 2 were preThe development of novel chiral ligands for applications in catalysis continues to be an important field of synthetic organic and organometallic chemistry [3] . Optically stable bidentate phosphanes exhibiting C 2 chirality in their carbon frameworks are among the most successful ligands employed in a variety of transition metal-catalyzed enantioselective hydrogenations [4] .…”

Formation of Diastereoisomerically Pure Oxazaphospholes and Their Reaction to Chiral Phosphane-Borane Adducts

“…For the best matching and selective recognition of the catalytically active transition-metal complex, bis[phosphanes] with a chiral backbone and equipped with additional centers of chirality at the P-atoms are of great interest. However, not many compounds of this class have been reported so far [8] [9] [12]. Therefore, it is important to further develop accessibility to asymmetrically substituted phosphines.…”