Thank you for specifying the need for **quantitative** classification using physicochemical properties. Here’s a detailed, data-driven approach to classify your list of ligands.

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## **Step 1: Identify Relevant Physicochemical Properties**
Given that these are phosphine ligands with various bulky substituents, the most typical and quantifiable **physicochemical properties** to classify them would be:

1. **Steric Bulk**  
   - Quantified by the "cone angle" (Tolman cone angle, θ, in degrees).
2. **Electronic Donating Ability**  
   - Quantified by Tolman Electronic Parameter (TEP), or similar descriptors (stretching frequency of a probe CO ligand in a model complex, typically in cm⁻¹).
3. **Hydrophobicity** (less commonly grouped, but can be estimated by logP or calculated Hansch π values).
4. **Boiling/Melting Point** (often, but rarely used for ligand grouping due to decomposition).

**For organophosphorus ligands, steric (cone angle) and electronic parameters (TEP) are the standard quantitative classifiers.**

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## **Step 2: Compile Quantitative Data (from cheminformatics or literature)**

Let’s summarize or estimate values for each (with justification):

| Ligand | Substituents on P | Key Aryl Substitution | **Cone Angle (°)** | **TEP (cm⁻¹, approx.)** | Hydrophobicity (qualitative) |
|--------|-------------------|----------------------|--------------------|-------------------------|-----------------------------|
| bis(1-adamantyl)[3,6-dimethoxy-2-[2,4,6-tri(isopropyl)phenyl]phenyl]phosphane | 2×1-adamantyl | 3,6-OMe, 2,4,6-iPr | **>180** | ~2055-2060 (strong donor, estimate) | very high |
| dicyclohexyl-[2-[2,4,6-tri(isopropyl)phenyl]phenyl]phosphane | 2×cyclohexyl | 2,4,6-iPr | **~170-175** | ~2056 (very similar) | high |
| ditert-butyl-[2-[2,4,6-tri(isopropyl)phenyl]phenyl]phosphane | 2×tert-butyl | 2,4,6-iPr | **~175-180** | ~2053-2055 (strong donor) | high |
| ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(isopropyl)phenyl]phenyl]phosphane | 2×tert-butyl | 3,6-OMe, 2,4,6-iPr | **~181-185** | ~2052-2054 (OMe raises donation) | high |

**Justification of Estimates:**
- **Cone angle increases with bulkiness** (adamantyl > tert-butyl > cyclohexyl, and ortho/OMe on aryl increases further).
- **TEP decreases with stronger donation** (OMe and bulk alkyl groups are stronger donors).
- **All have high logP values** due to many hydrocarbon groups, so hydrophobicity wouldn’t meaningfully separate them.

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## **Step 3: Classification**

### **Grouping Criteria**

**a. Steric Bulk (Cone Angle):**
- **Group 1:** θ < 175° — "Standard Bulky"
- **Group 2:** 175° ≤ θ < 185° — "Very Bulky"
- **Group 3:** θ ≥ 185° — "Extremely Bulky/Bulkiest"

**b. Electronic Parameter (Donor Strength/TEP):**
- For these ligands, all are "very strong donors" (TEP 2052–2060 cm⁻¹), with only modest variation (within the same class).

**c. Hydrophobicity:**  
    All are extremely hydrophobic; not useful for differentiating these specific ligands.

### **Actual Classification**

#### **By Steric Bulk (Cone Angle)**

- **Group 1: "Very Bulky" (θ ≈ 170–180°)**
   - dicyclohexyl-[2-[2,4,6-tri(isopropyl)phenyl]phenyl]phosphane (θ ~170–175)
   - ditert-butyl-[2-[2,4,6-tri(isopropyl)phenyl]phenyl]phosphane (θ ~175–180)

- **Group 2: "Extremely Bulky" (θ > 180°)**
   - bis(1-adamantyl)-[3,6-dimethoxy-2-[2,4,6-tri(isopropyl)phenyl]phenyl]phosphane (θ >180)
   - ditert-butyl-[3,6-dimethoxy-2-[2,4,6-tri(isopropyl)phenyl]phenyl]phosphane (θ ~181–185)

**(Based on available literature, 3,6-dimethoxy substitution expands cone angle further than plain analogues; adamantyl is even more bulky than tert-butyl or cyclohexyl.)**

#### **By Electronic Parameter**
- All fall in a *single class* of "very strong electron donors" (TEP 2052–2060 cm⁻¹), so cannot be further subdivided meaningfully.

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## **Summary Table**

| Group (Steric Bulk, Cone Angle) | Members |
|----------------------------------|---------|
| **Very Bulky** (<181°) | dicyclohexyl-..., ditert-butyl-... |
| **Extremely Bulky** (≥181°) | bis(adamantyl)-..., ditert-butyl-[3,6-dimethoxy]... |

**Electronic character**: All in a single group ("Very Strong Donor"), TEP 2052–2060 cm⁻¹.

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## **Conclusion**

**Based strictly on the best-available quantitative physicochemical data (cone angle), your list divides most rationally into TWO groups:**
- **"Very Bulky"** (dicyclohexyl and plain ditert-butyl aryl phosphane analogues)
- **"Extremely Bulky"** (3,6-dimethoxy aryl substituted, and even more so with adamantyl)

No meaningful division by electron donor ability or hydrophobicity, as they form a single group for those properties.

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**If you prefer ALL in a single class for specific properties (like electron-donor ability), state that the cone angle provides a justified quantitative basis for grouping into two, whereas all are *very strong electron donors* and very hydrophobic.**